SELECT

SELECT
    [ALL | DISTINCT | DISTINCTROW ]
    [HIGH_PRIORITY]
    [STRAIGHT_JOIN]
    [SQL_SMALL_RESULT] [SQL_BIG_RESULT] [SQL_BUFFER_RESULT]
    [SQL_CACHE | SQL_NO_CACHE] [SQL_CALC_FOUND_ROWS]
    select_expr [, select_expr] ...
    [into_option]
    [FROM table_references
      [PARTITION partition_list]]
    [WHERE where_condition]
    [GROUP BY {col_name | expr | position}
      [ASC | DESC], ... [WITH ROLLUP]]
    [HAVING where_condition]
    [ORDER BY {col_name | expr | position}
      [ASC | DESC], ...]
    [LIMIT {[offset,] row_count | row_count OFFSET offset}]
    [PROCEDURE procedure_name(argument_list)]
    [into_option]
    [FOR UPDATE | LOCK IN SHARE MODE]

into_option: {
    INTO OUTFILE 'file_name'
        [CHARACTER SET charset_name]
        export_options
  | INTO DUMPFILE 'file_name'
  | INTO var_name [, var_name] ...
}

SELECT ... INTO Statement

 SELECT ... INTO语句可以让查询结果存储到变量或者文件中：

Before FROM. Example:

SELECT * INTO @myvar FROM t1;

Before a trailing locking clause. Example:

SELECT * FROM t1 INTO @myvar FOR UPDATE;

SELECT id, data INTO @x, @y FROM test.t1 LIMIT 1;

SELECT a,b,a+b INTO OUTFILE '/tmp/result.txt'
  FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'
  LINES TERMINATED BY '
'
  FROM test_table;

 JOIN Clause

table_references:
    escaped_table_reference [, escaped_table_reference] ...

escaped_table_reference: {
    table_reference
  | { OJ table_reference }
}

table_reference: {
    table_factor
  | joined_table
}

table_factor: {
    tbl_name [PARTITION (partition_names)]
        [[AS] alias] [index_hint_list]
  | table_subquery [AS] alias
  | ( table_references )
}

joined_table: {
    table_reference [INNER | CROSS] JOIN table_factor [join_specification]
  | table_reference STRAIGHT_JOIN table_factor
  | table_reference STRAIGHT_JOIN table_factor ON search_condition
  | table_reference {LEFT|RIGHT} [OUTER] JOIN table_reference join_specification
  | table_reference NATURAL [{LEFT|RIGHT} [OUTER]] JOIN table_factor
}

join_specification: {
    ON search_condition
  | USING (join_column_list)
}

join_column_list:
    column_name [, column_name] ...

index_hint_list:
    index_hint [, index_hint] ...

index_hint: {
    USE {INDEX|KEY}
      [FOR {JOIN|ORDER BY|GROUP BY}] ([index_list])
  | {IGNORE|FORCE} {INDEX|KEY}
      [FOR {JOIN|ORDER BY|GROUP BY}] (index_list)
}

index_list:
    index_name [, index_name] ...

SELECT * FROM t1 LEFT JOIN (t2, t3, t4)
                 ON (t2.a = t1.a AND t3.b = t1.b AND t4.c = t1.c)

is equivalent to:

SELECT * FROM t1 LEFT JOIN (t2 CROSS JOIN t3 CROSS JOIN t4)
                 ON (t2.a = t1.a AND t3.b = t1.b AND t4.c = t1.c)

SELECT t1.name, t2.salary
  FROM employee AS t1 INNER JOIN info AS t2 ON t1.name = t2.name;

SELECT t1.name, t2.salary
  FROM employee t1 INNER JOIN info t2 ON t1.name = t2.name;

 UNION Clause

SELECT ...
UNION [ALL | DISTINCT] SELECT ...
[UNION [ALL | DISTINCT] SELECT ...]

mysql> SELECT 1, 2;
+---+---+
| 1 | 2 |
+---+---+
| 1 | 2 |
+---+---+
mysql> SELECT 'a', 'b';
+---+---+
| a | b |
+---+---+
| a | b |
+---+---+
mysql> SELECT 1, 2 UNION SELECT 'a', 'b';
+---+---+
| 1 | 2 |
+---+---+
| 1 | 2 |
| a | b |
+---+---+