mysql select语句操作实例

Select的语法

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, ...
    [INTO OUTFILE 'file_name' export_options
      | INTO DUMPFILE 'file_name']
    [FROM table_references
    [WHERE where_definition]
    [GROUP BY {col_name | expr | position}
      [ASC | DESC], ... [WITH ROLLUP]]
    [HAVING where_definition]
    [ORDER BY {col_name | expr | position}
      [ASC | DESC] , ...]
    [LIMIT {[offset,] row_count | row_count OFFSET offset}]
    [PROCEDURE procedure_name(argument_list)]
    [FOR UPDATE | LOCK IN SHARE MODE]]

SELECT用于恢复从一个或多个表中选择的行，并可以加入UNION语句和子查询。

每个select_expr都指示一个您想要恢复的列， table_references指示行从哪个表或哪些表中被恢复。

简单查询

SELECT columna columnb FROM mytable;

ORDER BY查询

SELECT college, region, seed FROM tournament  ORDER BY region, seed;
SELECT college, region AS r, seed AS s FROM tournament ORDER BY r, s;
SELECT college, region, seed FROM tournament  ORDER BY 2, 3;

--要以相反的顺序进行分类，应把DESC（降序）关键字添加到ORDER BY子句中的列名称中。默认值为升序；该值可以使用ASC关键词明确地指定。
SELECT a, COUNT(b) FROM test_table ORDER BY a DESC；

GROUP BY查询

SELECT a, COUNT(b) FROM test_table GROUP BY a DESC；
SELECT COUNT(col1) AS col2 FROM t GROUP BY col2 HAVING col2 = 2;

-- HAVING不能用于应被用于WHERE子句的条目,不能编写如下语句：
SELECT col_name FROM tbl_name HAVING col_name > 0;
--而应该这么编写
SELECT col_name FROM tbl_name WHERE col_name > 0;

--HAVING子句可以引用总计函数，而WHERE子句不能引用：
SELECT user, MAX(salary) FROM users GROUP BY user HAVING MAX(salary)>10;

LIMIT查询

SELECT * FROM tbl LIMIT 10;  # Retrieve rows 0-9;
SELECT * FROM tbl LIMIT 5,10;  # Retrieve rows 6-15;

--如果要恢复从某个偏移量到结果集合的末端之间的所有的行，您可以对第二个参数是使用比较大的数。
--以下语句可以恢复从第96行到最后的所有行：
SELECT * FROM tbl LIMIT 95,18446744073709551615;

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