注意
想法及时记录，实现可以待做。
SQL语句主要可以分为DDL、DML、DCL几大类。
DML（Data Manipulation Language）语句：数据操纵语句，用于添加、删除、更新和查询数据库记录，并检查数据完整性，常用的语句关键字主要包括 insert、delete、update 和select等。
查询语句
查询语句的语法
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 [, 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] ...
}
简单的查询
SELECT CONCAT(last_name,', ',first_name) AS full_name
FROM mytable ORDER BY full_name;
join
SELECT * FROM t1 LEFT JOIN (t2, t3, t4)
ON (t2.a = t1.a AND t3.b = t1.b AND t4.c = t1.c)
上述语句与下述语句等价。
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)
对于MySQL，JOIN、CROSS JOIN、INNER JOIN在语法上是等价的。在标准SQL语法中，他们却不是等价的，这点尤其要注意。
union
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 |
+---+---+
合并结果集，然后排序或者limit都可以。
(SELECT a FROM t1 WHERE a=10 AND B=1)
UNION
(SELECT a FROM t2 WHERE a=11 AND B=2)
ORDER BY a LIMIT 10;
子查询
SELECT * FROM t1
WHERE column1 = (SELECT MAX(column2) FROM t2);
SELECT s1 FROM t1 WHERE s1 = ANY (SELECT s1 FROM t2);
SELECT s1 FROM t1 WHERE s1 IN (SELECT s1 FROM t2);
SELECT column1 FROM t1 WHERE EXISTS (SELECT * FROM t2);
查看数据库的大小分布
select
table_schema as '数据库',
sum(table_rows) as '记录数',
sum(truncate(data_length/1024/1024, 2)) as '数据容量(MB)',
sum(truncate(index_length/1024/1024, 2)) as '索引容量(MB)'
from information_schema.tables
group by table_schema
order by sum(data_length) desc, sum(index_length) desc;
select
table_schema as '数据库',
table_name as '表名',
table_rows as '记录数',
truncate(data_length/1024/1024, 2) as '数据容量(MB)',
truncate(index_length/1024/1024, 2) as '索引容量(MB)'
from information_schema.tables
where table_schema='test'
order by data_length desc, index_length desc;
修改数据
更新语句的语法
UPDATE [LOW_PRIORITY] [IGNORE] table_reference
SET assignment_list
[WHERE where_condition]
[ORDER BY ...]
[LIMIT row_count]
value:
{expr | DEFAULT}
assignment:
col_name = value
assignment_list:
assignment [, assignment] ...
UPDATE `test` SET `operation` = replace (`operation`,'测试','demo') WHERE `operation` LIKE '%测试%';
UPDATE items,
(SELECT id FROM items
WHERE id IN
(SELECT id FROM items
WHERE retail / wholesale >= 1.3 AND quantity < 100))
AS discounted
SET items.retail = items.retail * 0.9
WHERE items.id = discounted.id;
新增数据
新增语句的语法
INSERT [LOW_PRIORITY | DELAYED | HIGH_PRIORITY] [IGNORE]
[INTO] tbl_name
[PARTITION (partition_name [, partition_name] ...)]
[(col_name [, col_name] ...)]
{VALUES | VALUE} (value_list) [, (value_list)] ...
[ON DUPLICATE KEY UPDATE assignment_list]
INSERT [LOW_PRIORITY | DELAYED | HIGH_PRIORITY] [IGNORE]
[INTO] tbl_name
[PARTITION (partition_name [, partition_name] ...)]
SET assignment_list
[ON DUPLICATE KEY UPDATE assignment_list]
INSERT [LOW_PRIORITY | HIGH_PRIORITY] [IGNORE]
[INTO] tbl_name
[PARTITION (partition_name [, partition_name] ...)]
[(col_name [, col_name] ...)]
SELECT ...
[ON DUPLICATE KEY UPDATE assignment_list]
value:
{expr | DEFAULT}
value_list:
value [, value] ...
assignment:
col_name = value
assignment_list:
assignment [, assignment] ...
INSERT INTO tbl_name (a,b,c) VALUES(1,2,3),(4,5,6),(7,8,9);
删除数据
删除语句的语法
DELETE [LOW_PRIORITY] [QUICK] [IGNORE] FROM tbl_name
[PARTITION (partition_name [, partition_name] ...)]
[WHERE where_condition]
[ORDER BY ...]
[LIMIT row_count]
DELETE FROM somelog WHERE user = 'jcole'
ORDER BY timestamp_column LIMIT 1;
DELETE t1 FROM t1 LEFT JOIN t2 ON t1.id=t2.id WHERE t2.id IS NULL;
