postgres 查询表的大小 清空表

查询表中数据大小：

--数据库中单个表的大小（不包含索引）

select pg_size_pretty(pg_relation_size('表名'));

--查出所有表（包含索引）并排序
SELECT table_schema || '.' || table_name AS table_full_name, pg_size_pretty(pg_total_relation_size('"' || table_schema || '"."' || table_name || '"')) AS size
FROM information_schema.tables
ORDER BY
pg_total_relation_size('"' || table_schema || '"."' || table_name || '"') DESC limit 20

--查出表大小按大小排序并分离data与index
SELECT
table_name,
pg_size_pretty(table_size) AS table_size,
pg_size_pretty(indexes_size) AS indexes_size,
pg_size_pretty(total_size) AS total_size
FROM (
SELECT
table_name,
pg_table_size(table_name) AS table_size,
pg_indexes_size(table_name) AS indexes_size,
pg_total_relation_size(table_name) AS total_size
FROM (
SELECT ('"' || table_schema || '"."' || table_name || '"') AS table_name
FROM information_schema.tables
) AS all_tables
ORDER BY total_size DESC
) AS pretty_sizes

删除表中数据：

1.适用数据量较小的情况

delete from tablename;

2.适合删除大量数据，速度快

TRUNCATE TABLE tablename;

3.若该表有外键，要用级联方式删所有关联的数据

TRUNCATE TABLE tablename CASCADE;

直接删表：

drop table if exists +表名