5.常用函数
函数可以进行字符串的处理、数值计算和日期计算等，mysql可以用在SQL(DML)中以增加SQL的功能。
5.1 数值函数
1. abs(x) 返回x的绝对值
select abs(5),abs(-5);
2. ceil(x) 向上取整
select ceil(5.01),ceil(-5.01); -- 正负号结果不一致
3. floor(x) 向下取整
select floor(5.98),floor(-5.98); -- 正负号结果不一致
4. mod(x,y) 返回x除以y的余数
select mod(7,4);
5. rand() 返回0~1内的随机值
select rand(),rand();
6. round(x,y) 返回对x保留y位小数后的四舍五入结果
select round(123.456,2),round(-123.456,2); -- 正负号结果一致
7. truncate(x,y) 返回对x保留y位小数后的截断结果
select truncate(123.456,2),truncate(-123.456,2); -- 正负号结果一致
5.2 字符串函数
1.concat(s1,s2,...,sn) 连接n个字符串
select concat('hello ','mysql ','database');
2.concat_ws(d,s1,s2,...,sn) 连接n个字符串,并指定连接符
select concat_ws(' ','hello','mysql','database');
3.insert(str,x,y,instr) 将字符串str从第x位置开始，y个字符串长的子串替换为字符串instr
select insert('ABCDEFG',2,3,'123');
4.lower(str) 将字符串str中所有字符转为小写字符
select lower('ABCDEFG');
5.upper(str) 将字符串str中所有字符转为大写字符
select upper('abCD12fG');
6.left(str,x) 返回字符串str中最左边的x个字符
select left('ABCDEFG',3);
7.right(str,x) 返回字符串str中最右边的x个字符
select right('ABCDEFG',3);
8.lpad(str,n,pad) 用字符串pad对str最左边进行填充，直到长度为n个字符长度
select lpad('ABCDEFG',10,'*');
9.rpad(str,n,pad) 用字符串pad对str最右边进行填充，直到长度为n个字符长度
select rpad('ABCDEFG',10,'*');
10.trim(str) 去掉字符串左右两端的空格，并返回
select trim(' ABC DEFG ');
11.ltrim(str) 去掉字符串左侧的空格，并返回
select ltrim(' ABC DEFG ');
12.rtrim(str) 去掉字符串右侧的空格，并返回
select rtrim(' ABC DEFG ');
13.instr(str,x) 从str字符串中查找x子字符串，找到则返回x子字符串首字母在str字符串中的位置，未找到则返回0
select instr('ABCDEFG','CD'); -- 3
select instr('ABCDEFG','DC'); -- 0
14.repeat(str,x) 返回str重复x次的结果
select repeat('ABC',3);
15.replace(str,a,b) 用b字符串替换str字符串中的a字符串。
select replace('ABCDEFG','ABC','123');
select replace(' ABC DEFG ',' ','');
16.strcmp(s1,s2) 从首字母开始比较字符串s1和s2的ASCII码值的大小，0相等，1大于，-1小于
select strcmp('ABC','ABC'); -- 0
select strcmp('ABC','abc'); -- 0 不区分大小写
select strcmp('BC','AD'); -- 1 首字母不同时比较首字母
select strcmp('BC','BB'); -- 1 首字母相同时比较后续字母
select strcmp('AB','BB'); -- -1
17.substring(str,x,y) 返回str中从x位置开始的y位长度子串
select substring('ABCDEFG',1,3); -- ABC
select substring('ABCDEFG',0,3); -- null
select substring('ABCDEFG',6,3); -- FG
select substring('ABCDEFG',-1,3); -- G
select substring('ABCDEFG',-6,3); -- BCD
5.3 日期和时间函数
1.curdate() 返回当前日期(年月日)
2.curtime() 返回当前时间(时分秒)
3.now() 返回当前日期时间(年月日时分秒)
select curdate(),curtime(),now();
4.unix_timestamp(date) 返回日期date的unix时间戳
select unix_timestamp(now()); -- 1535008983
5.from_unixtime(n) 返回unix时间戳对应的日期值
select from_unixtime(1535008983); -- '2018-08-23 15:23:03'
6.year(date) 返回日期date的年
7.month(date) 返回日期date的月
8.day(date) 返回日期date的日
9.hour(date) 返回日期date的时
10.minute(date) 返回日期date的分
11.second(date) 返回日期date的秒
select year(now()),month(now()),day(now()),hour(now()),minute(now()),second(now());
12.week(date) 返回日期date是本年的第几周
select week(now());
13.monthname(date) 返回日期date所在月份的月份名
select monthname(now());
14.date_format(date,fmt) 返回按字符串fmt格式化的日期字符串
select date_format(now(),'%Y-%m-%d %H:%i:%s');
select date_format(now(),'%Y年%m月%d日%H时%i分%s秒');
15.date_add(date,interval expr type) 返回日期date加上时间间隔interval expr type后的日期值
select date_add(now(),interval 1 year),date_add(now(),interval 2 month),date_add(now(),interval 3 day),date_add(now(),interval 4 hour),date_add(now(),interval 5 minute),date_add(now(),interval 6 second);
select date_add(now(),interval '1_2' year_month); -- 增加1年2月
select date_add(now(),interval '2_3' month_day); -- 1064
select date_add(now(),interval '3_4' day_hour); -- 增加3天4小时
select date_add(now(),interval '3_4_5' day_minute); -- 增加3天4小时5分
select date_add(now(),interval '3_4_5_6' day_second); -- 增加3天4小时5分6秒
select date_add(now(),interval '4_5' hour_minute); -- 增加4小时5分
select date_add(now(),interval '4_5_6' hour_second); -- 增加4小时5分6秒
select date_add(now(),interval '5_6' minute_second); -- 增加5分6秒
select date_add(now(),interval -1 year); -- 可以使用负数，表示减去一个时间间隔返回之前的耨个日期
16.datediff(date1,date2) 计算两个日期之间相差的天数
select datediff(now(),date_add(now(),interval '-1_2' year_month)); -- 相差1年2月，大致为365+61=426
select datediff(now(),'2008-08-08'); -- 当前日期减去特定日期的天数
select datediff('2008-08-08',now()); -- 可以为负值
5.4 流程函数
流程函数跟条件选择相关，可以分支功能。
1.if(value,t,f) 如果value为真，则返回t,否则返回f
select *,if(sal>2500,'good','bad') from emp;
2.ifnull(value1,value2) 如果value1不为空，则返回value1,否则返回value2
select *,sal+ifnull(comm,0) from emp;
3.case when [value1] then [result1]...else [default] end 如果value1为真，则返回result1,否则返回default
select *,case when sal>=3000 then 'high' when sal>=1500 then 'medium' else 'low' end from emp;
4.case [expr] when [value1] then [result1]...else [default] end 如果expr=value1，则返回result1,否则返回default
select *,case deptno when 10 then 'ACCOUNTING' when 20 then 'RESEARCH' when 30 then 'SALES' when 40 then 'OPERATIONS' else '' end from emp;
5.decode() 尚不清楚具体用途
select *,decode(deptno,10) dname from emp;
5.5 其他常用函数
1.database() 返回当前数据库名
2.version() 返回当前数据库版本 5.7.22-log
3.user() 返回当前登录用户名
select database(),version(),user();
4.inet_aton(IP) 返回IP地址的数字表示，用于进行IP范围比较
5.inet_ntoa(num) 返回数字代表的IP地址
select inet_aton('192.168.1.125'),inet_ntoa(inet_aton('192.168.1.125'));
6.password(str) 返回字符串str的加密版本，用于设置mysql用户密码，返回41位长的字符串
7.md5(str) 返回字符串str的MD5值,用于对应用数据加密
select password('abc@123'),md5('abc@123');
5.6 小结
mysql keyw --> keyword 关键字
mysql libf --> library function 库函数（内置函数）
mysql svar --> System variable 系统变量
mysql uvar --> User variable 用户自定义变量
mysql scma --> schema 模式
1.keyword 关键字
all
avg
bit_and
bit_or
bit_xor
case
cast
convert
count
date
default
distinct
distinctrow
exists
false
float_number
group_concat
high_priority
interval
match
max
min
not
null
row
sql_big_result
sql_buffer_result
sql_cache
sql_calc_found_rows
sql_no_cache
sql_small_result
std
stddev
stddev_samp
straight_join
sum
time
timestamp
true
values
var_pop
var_samp
variance
2.library function 库函数（内置函数）
abs()
acos()
adddate()
addtime()
aes_decrypt()
aes_encrypt()
area()
asbinary()
ascii()
asin()
astext()
atan()
atan2()
avg()
benchmark()
bin()
bit_and()
bit_count()
bit_length()
bit_or()
bit_xor()
boundary()
buffer()
cast()
ceil()
ceiling()
char()
char_length()
character_length()
charset()
coalesce()
coercibility()
collation()
compress()
concat()
concat_ws()
connection_id()
contains()
conv()
convert()
convert_tz()
cos()
cot()
count()
crc32()
crosses()
curdate()
current_date()
current_time()
current_timestamp()
curtime()
database()
date()
date_add()
date_format()
date_sub()
datediff()
day()
dayname()
dayofmonth()
dayofweek()
dayofyear()
decode()
default()
degrees()
des_decrypt()
des_encrypt()
dimension()
disjoint()
elt()
encode()
encrypt()
endpoint()
envelope()
equals()
exp()
export_set()
exteriorring()
extract()
extractvalue()
field()
find_in_set()
floor()
format()
found_rows()
from_base64()
from_days()
from_unixtime()
geomcollfromtext()
geomcollfromwkb()
geometrycollection()
geometryn()
geometrytype()
geomfromtext()
geomfromwkb()
get_format()
get_lock()
glength()
greatest()
group_concat()
gtid_subset()
gtid_subtract()
hex()
hour()
if()
ifnull()
inet6_aton()
inet6_ntoa()
inet_aton()
inet_ntoa()
insert()
instr()
interiorringn()
intersects()
interval()
ipv4_compat()
is_free_lock()
is_ipv4()
is_ipv4_mapped()
is_ipv6()
is_used_lock()
isclosed()
isempty()
isnull()
issimple()
last_insert_id()
lcase()
least()
left()
length()
lineformtext()
lineformwkb()
linestring()
ln()
load_file()
localtime()
localtimestamp()
locate()
log()
log10()
log2()
lower()
lpad()
ltrim()
make_set()
makedate()
maketime()
master_pos_wait()
max()
mbrcontains()
mbrdisjoint()
mbrequal()
mbrintersects()
mbroverlaps()
mbrtouches()
mbrwithin()
md5()
microsecond()
mid()
min()
minute()
mlineformtext()
mlinefromwkb()
mod()
month()
monthname()
mpointfromtext()
mpointfromwkb()
mpolyfromtext()
mpolyfromwkb()
multilinestring()
multipoint()
multipolygon()
name_const()
now()
nullif()
numgeometries()
numinteriorrings()
numpoints()
oct()
octet_length()
old_password()
ord()
over_laps()
password()
period_add()
period_diff()
pi()
point()
pointfromtext()
pointfromwkb()
pointn()
polyfromtext()
polyfromwkb()
polygon()
position()
pow()
power()
quarter()
quote()
radians()
rand()
random_bytes()
release_lock()
repeat()
replace()
reverse()
right()
round()
row_count()
rpad()
rtrim()
schema()
sec_to_time()
second()
session_user()
sha()
sha1()
sha2()
sign()
sin()
sleep()
soundex()
space()
sqrt()
srid()
st_contains()
st_crosses()
st_disjoint()
st_equals()
st_intersects()
st_touches()
st_within()
startpoint()
std()
stddev()
stddev_pop()
stddev_samp()
str_to_date()
strcmp()
subdate()
substr()
substring()
substring_index2()
subtime()
sum()
sysdate()
system_user()
tan()
time()
time_format()
time_to_sec()
timediff()
timestamp()
timestampadd()
timestampdiff()
to_base64()
to_days()
to_seconds()
touches()
trim()
truncate()
ucase()
uncompress()
uncompress_length()
unhex()
unix_timestamp()
updatexml()
upper()
user()
utc_date()
utc_time()
utc_timestamp()
uuid()
uuid_short()
validate_password_strength()
values()
var_pop()
var_samp()
variance()
version()
wait_until_sql_thread_after_gtids()
week()
weekday()
weekofyear()
weight_string()
within()
x()
y()
year()
yearweek()
3.System variable 系统变量
@@auto_increment_increment
@@auto_increment_offset
@@autocommit
@@automatic_sp_privileges
@@avoid_temporal_upgrade
@@back_log
@@basedir
@@big_tables
@@bind_address
@@binlog_cache_size
@@binlog_checksum
@@binlog_direct_non_transactional_updates
@@binlog_error_action
@@binlog_format
@@binlog_group_commit_sync_delay
@@binlog_group_commit_sync_no_delay_count
@@binlog_gtid_simple_recovery
@@binlog_max_flush_queue_time
@@binlog_order_commits
@@binlog_row_image
@@binlog_rows_query_log_events
@@binlog_stmt_cache_size
@@binlog_transaction_dependency_history_size
@@binlog_transaction_dependency_tracking
@@block_encryption_mode
@@bulk_insert_buffer_size
@@character_set_client
@@character_set_connection
@@character_set_database
@@character_set_filesystem
@@character_set_results
@@character_set_server
@@character_set_system
@@character_sets_dir
@@check_proxy_users
@@collation_connection
@@collation_database
@@collation_server
@@completion_type
@@concurrent_insert
@@connect_timeout
@@core_file
@@datadir
@@date_format
@@datetime_format
@@default_authentication_plugin
@@default_password_lifetime
@@default_storage_engine
@@default_tmp_storage_engine
@@default_week_format
@@delay_key_write
@@delayed_insert_limit
@@delayed_insert_timeout
@@delayed_queue_size
@@disabled_storage_engines
@@disconnect_on_expired_password
@@div_precision_increment
@@end_markers_in_json
@@enforce_gtid_consistency
@@eq_range_index_dive_limit
@@error_count
@@event_scheduler
@@expire_logs_days
@@explicit_defaults_for_timestamp
@@external_user
@@flush
@@flush_time
@@foreign_key_checks
@@ft_boolean_syntax
@@ft_max_word_len
@@ft_min_word_len
@@ft_query_expansion_limit
@@ft_stopword_file
@@general_log
@@general_log_file
@@group_concat_max_len
@@gtid_executed_compression_period
@@gtid_mode
@@gtid_next
@@gtid_owned
@@gtid_purged
@@have_compress
@@have_crypt
@@have_dynamic_loading
@@have_geometry
@@have_openssl
@@have_profiling
@@have_query_cache
@@have_rtree_keys
@@have_ssl
@@have_statement_timeout
@@have_symlink
@@host_cache_size
@@hostname
@@identity
@@ignore_builtin_innodb
@@ignore_db_dirs
@@init_connect
@@init_file
@@init_slave
@@innodb_adaptive_flushing
@@innodb_adaptive_flushing_lwm
@@innodb_adaptive_hash_index
@@innodb_adaptive_hash_index_parts
@@innodb_adaptive_max_sleep_delay
@@innodb_api_bk_commit_interval
@@innodb_api_disable_rowlock
@@innodb_api_enable_binlog
@@innodb_api_enable_mdl
@@innodb_api_trx_level
@@innodb_autoextend_increment
@@innodb_autoinc_lock_mode
@@innodb_buffer_pool_chunk_size
@@innodb_buffer_pool_dump_at_shutdown
@@innodb_buffer_pool_dump_now
@@innodb_buffer_pool_dump_pct
@@innodb_buffer_pool_filename
@@innodb_buffer_pool_instances
@@innodb_buffer_pool_load_abort
@@innodb_buffer_pool_load_at_startup
@@innodb_buffer_pool_load_now
@@innodb_buffer_pool_size
@@innodb_change_buffer_max_size
@@innodb_change_buffering
@@innodb_checksum_algorithm
@@innodb_checksums
@@innodb_cmp_per_index_enabled
@@innodb_commit_concurrency
@@innodb_compression_failure_threshold_pct
@@innodb_compression_level
@@innodb_compression_pad_pct_max
@@innodb_concurrency_tickets
@@innodb_data_file_path
@@innodb_data_home_dir
@@innodb_deadlock_detect
@@innodb_default_row_format
@@innodb_disable_sort_file_cache
@@innodb_doublewrite
@@innodb_fast_shutdown
@@innodb_file_format
@@innodb_file_format_check
@@innodb_file_format_max
@@innodb_file_per_table
@@innodb_fill_factor
@@innodb_flush_log_at_timeout
@@innodb_flush_log_at_trx_commit
@@innodb_flush_method
@@innodb_flush_neighbors
@@innodb_flush_sync
@@innodb_flushing_avg_loops
@@innodb_force_load_corrupted
@@innodb_force_recovery
@@innodb_ft_aux_table
@@innodb_ft_cache_size
@@innodb_ft_enable_diag_print
@@innodb_ft_enable_stopword
@@innodb_ft_max_token_size
@@innodb_ft_min_token_size
@@innodb_ft_num_word_optimize
@@innodb_ft_result_cache_limit
@@innodb_ft_server_stopword_table
@@innodb_ft_sort_pll_degree
@@innodb_ft_total_cache_size
@@innodb_ft_user_stopword_table
@@innodb_io_capacity
@@innodb_io_capacity_max
@@innodb_large_prefix
@@innodb_lock_wait_timeout
@@innodb_locks_unsafe_for_binlog
@@innodb_log_buffer_size
@@innodb_log_checksums
@@innodb_log_compressed_pages
@@innodb_log_file_size
@@innodb_log_files_in_group
@@innodb_log_group_home_dir
@@innodb_log_write_ahead_size
@@innodb_lru_scan_depth
@@innodb_max_dirty_pages_pct
@@innodb_max_dirty_pages_pct_lwm
@@innodb_max_purge_lag
@@innodb_max_purge_lag_delay
@@innodb_max_undo_log_size
@@innodb_monitor_disable
@@innodb_monitor_enable
@@innodb_monitor_reset
@@innodb_monitor_reset_all
@@innodb_old_blocks_pct
@@innodb_old_blocks_time
@@innodb_online_alter_log_max_size
@@innodb_open_files
@@innodb_optimize_fulltext_only
@@innodb_page_cleaners
@@innodb_page_size
@@innodb_print_all_deadlocks
@@innodb_purge_batch_size
@@innodb_purge_rseg_truncate_frequency
@@innodb_purge_threads
@@innodb_random_read_ahead
@@innodb_read_ahead_threshold
@@innodb_read_io_threads
@@innodb_read_only
@@innodb_replication_delay
@@innodb_rollback_on_timeout
@@innodb_rollback_segments
@@innodb_sort_buffer_size
@@innodb_spin_wait_delay
@@innodb_stats_auto_recalc
@@innodb_stats_include_delete_marked
@@innodb_stats_method
@@innodb_stats_on_metadata
@@innodb_stats_persistent
@@innodb_stats_persistent_sample_pages
@@innodb_stats_sample_pages
@@innodb_stats_transient_sample_pages
@@innodb_status_output
@@innodb_status_output_locks
@@innodb_strict_mode
@@innodb_support_xa
@@innodb_sync_array_size
@@innodb_sync_spin_loops
@@innodb_table_locks
@@innodb_temp_data_file_path
@@innodb_thread_concurrency
@@innodb_thread_sleep_delay
@@innodb_tmpdir
@@innodb_undo_directory
@@innodb_undo_log_truncate
@@innodb_undo_logs
@@innodb_undo_tablespaces
@@innodb_use_native_aio
@@innodb_version
@@innodb_write_io_threads
@@insert_id
@@interactive_timeout
@@internal_tmp_disk_storage_engine
@@join_buffer_size
@@keep_files_on_create
@@key_buffer_size
@@key_cache_age_threshold
@@key_cache_block_size
@@key_cache_division_limit
@@keyring_operations
@@large_files_support
@@large_page_size
@@large_pages
@@last_insert_id
@@lc_messages
@@lc_messages_dir
@@lc_time_names
@@license
@@local_infile
@@lock_wait_timeout
@@log_bin
@@log_bin_basename
@@log_bin_index
@@log_bin_trust_function_creators
@@log_bin_use_v1_row_events
@@log_builtin_as_identified_by_password
@@log_error
@@log_error_verbosity
@@log_output
@@log_queries_not_using_indexes
@@log_slave_updates
@@log_slow_admin_statements
@@log_slow_slave_statements
@@log_statements_unsafe_for_binlog
@@log_syslog
@@log_syslog_tag
@@log_throttle_queries_not_using_indexes
@@log_timestamps
@@log_warnings
@@long_query_time
@@low_priority_updates
@@lower_case_file_system
@@lower_case_table_names
@@master_info_repository
@@master_verify_checksum
@@max_allowed_packet
@@max_binlog_cache_size
@@max_binlog_size
@@max_binlog_stmt_cache_size
@@max_connect_errors
@@max_connections
@@max_delayed_threads
@@max_digest_length
@@max_error_count
@@max_execution_time
@@max_heap_table_size
@@max_insert_delayed_threads
@@max_join_size
@@max_length_for_sort_data
@@max_points_in_geometry
@@max_prepared_stmt_count
@@max_relay_log_size
@@max_seeks_for_key
@@max_sort_length
@@max_sp_recursion_depth
@@max_tmp_tables
@@max_user_connections
@@max_write_lock_count
@@metadata_locks_cache_size
@@metadata_locks_hash_instances
@@min_examined_row_limit
@@multi_range_count
@@myisam_data_pointer_size
@@myisam_max_sort_file_size
@@myisam_mmap_size
@@myisam_recover_options
@@myisam_repair_threads
@@myisam_sort_buffer_size
@@myisam_stats_method
@@myisam_use_mmap
@@mysql_native_password_proxy_users
@@named_pipe
@@net_buffer_length
@@net_read_timeout
@@net_retry_count
@@net_write_timeout
@@new
@@ngram_token_size
@@offline_mode
@@old
@@old_alter_table
@@old_passwords
@@open_files_limit
@@optimizer_prune_level
@@optimizer_search_depth
@@optimizer_switch
@@optimizer_trace
@@optimizer_trace_features
@@optimizer_trace_limit
@@optimizer_trace_max_mem_size
@@optimizer_trace_offset
@@parser_max_mem_size
@@performance_schema
@@performance_schema_accounts_size
@@performance_schema_digests_size
@@performance_schema_events_stages_history_long_size
@@performance_schema_events_stages_history_size
@@performance_schema_events_statements_history_long_size
@@performance_schema_events_statements_history_size
@@performance_schema_events_transactions_history_long_size
@@performance_schema_events_transactions_history_size
@@performance_schema_events_waits_history_long_size
@@performance_schema_events_waits_history_size
@@performance_schema_hosts_size
@@performance_schema_max_cond_classes
@@performance_schema_max_cond_instances
@@performance_schema_max_digest_length
@@performance_schema_max_file_classes
@@performance_schema_max_file_handles
@@performance_schema_max_file_instances
@@performance_schema_max_index_stat
@@performance_schema_max_memory_classes
@@performance_schema_max_metadata_locks
@@performance_schema_max_mutex_classes
@@performance_schema_max_mutex_instances
@@performance_schema_max_prepared_statements_instances
@@performance_schema_max_program_instances
@@performance_schema_max_rwlock_classes
@@performance_schema_max_rwlock_instances
@@performance_schema_max_socket_classes
@@performance_schema_max_socket_instances
@@performance_schema_max_sql_text_length
@@performance_schema_max_stage_classes
@@performance_schema_max_statement_classes
@@performance_schema_max_statement_stack
@@performance_schema_max_table_handles
@@performance_schema_max_table_instances
@@performance_schema_max_table_lock_stat
@@performance_schema_max_thread_classes
@@performance_schema_max_thread_instances
@@performance_schema_session_connect_attrs_size
@@performance_schema_setup_actors_size
@@performance_schema_setup_objects_size
@@performance_schema_users_size
@@pid_file
@@plugin_dir
@@port
@@preload_buffer_size
@@profiling
@@profiling_history_size
@@protocol_version
@@proxy_user
@@pseudo_slave_mode
@@pseudo_thread_id
@@query_alloc_block_size
@@query_cache_limit
@@query_cache_min_res_unit
@@query_cache_size
@@query_cache_type
@@query_cache_wlock_invalidate
@@query_prealloc_size
@@rand_seed1
@@rand_seed2
@@range_alloc_block_size
@@range_optimizer_max_mem_size
@@rbr_exec_mode
@@read_buffer_size
@@read_only
@@read_rnd_buffer_size
@@relay_log
@@relay_log_basename
@@relay_log_index
@@relay_log_info_file
@@relay_log_info_repository
@@relay_log_purge
@@relay_log_recovery
@@relay_log_space_limit
@@report_host
@@report_password
@@report_port
@@report_user
@@require_secure_transport
@@rpl_stop_slave_timeout
@@secure_auth
@@secure_file_priv
@@server_id
@@server_id_bits
@@server_uuid
@@session_track_gtids
@@session_track_schema
@@session_track_state_change
@@session_track_system_variables
@@session_track_transaction_info
@@sha256_password_proxy_user
@@shared_memory
@@shared_memory_base_name
@@show_compatibility_56
@@show_create_table_verbosity
@@show_old_temporals
@@skip_external_locking
@@skip_name_resolve
@@skip_networking
@@skip_show_database
@@slave_allow_batching
@@slave_checkpoint_group
@@slave_checkpoint_period
@@slave_compressed_protocol
@@slave_exec_mode
@@slave_load_tmpdir
@@slave_max_allowed_packet
@@slave_net_timeout
@@slave_parallel_type
@@slave_parallel_workers
@@slave_pending_jobs_size_max
@@slave_preserve_commit_order
@@slave_rows_search_algorithms
@@slave_skip_errors
@@slave_sql_verify_checksum
@@slave_transaction_retries
@@slave_type_conversions
@@slow_launch_time
@@slow_query_log
@@slow_query_log_file
@@socket
@@sort_buffer_size
@@sql_auto_is_null
@@sql_big_selects
@@sql_buffer_result
@@sql_log_bin
@@sql_log_off
@@sql_mode
@@sql_notes
@@sql_quote_show_create
@@sql_safe_updates
@@sql_select_limit
@@sql_slave_skip_counter
@@sql_warnings
@@ssl_ca
@@ssl_capath
@@ssl_cert
@@ssl_cipher
@@ssl_crl
@@ssl_crlpath
@@ssl_key
@@stored_program_cache
@@super_read_only
@@sync_binlog
@@sync_frm
@@sync_master_info
@@sync_relay_log
@@sync_relay_log_info
@@system_time_zone
@@table_definition_cache
@@table_open_cache
@@table_open_cache_instances
@@thread_cache_size
@@thread_handling
@@thread_stack
@@time_fromat
@@time_zone
@@timestamp
@@tls_version
@@tmp_table_size
@@tmpdir
@@transaction_alloc_block_size
@@transaction_allow_batching
@@transaction_isolation
@@transaction_prealloc_size
@@transaction_read_only
@@transaction_write_set_extraction
@@tx_isolation
@@tx_read_only
@@unique_checks
@@updatable_views_with_limit
@@version
@@version_comment
@@version_compile_machine
@@version_compile_os
@@wait_timeout
@@warning_count