【SQL基础语法】
1.Select 查询所有列
SELECT * FROM mytable（表名）;
SELECT column（列名）, another_column, … FROM mytable（表名）;
2.Where条件查询语法（大小写都可以，键值对的值需要引号括起来）
SELECT column, another_column, …
FROM mytable
WHERE condition
AND/OR another_condition AND/OR …;
| Operator（关键字） | Condition（意思） | SQL Example(例子） |
| =, !=, < <=, >, >= | Standard numerical operators 基础的 大于，等于等比较 | col_name != 4 |
| BETWEEN … AND … | Number is within range of two values (inclusive) 在两个数之间 | col_name BETWEEN 1.5 AND 10.5 |
| NOT BETWEEN … AND … | Number is not within range of two values (inclusive) 不在两个数之间 | col_name NOT BETWEEN 1 AND 10 |
| IN (…) | Number exists in a list 在一个列表 | col_name IN (2, 4, 6) |
| NOT IN (…) | Number does not exist in a list 不在一个列表 | col_name NOT IN (1, 3, 5) |
| Operator（操作符） | Condition（解释） | Example（例子） |
| = | Case sensitive exact string comparison (notice the single equals)完全等于 | col_name = "abc" |
| != or <> | Case sensitive exact string inequality comparison 不等于 | col_name != "abcd" |
| LIKE | Case insensitive exact string comparison 没有用通配符等价于 = | col_name LIKE "ABC" |
| NOT LIKE | Case insensitive exact string inequality comparison 没有用通配符等价于 != | col_name NOT LIKE "ABCD" |
| % | Used anywhere in a string to match a sequence of zero or more characters (only with LIKE or NOT LIKE) 通配符，代表匹配0个以上的字符 | col_name LIKE "%AT%" (matches "AT", "ATTIC", "CAT" or even "BATS") "%AT%" 代表AT 前后可以有任意字符 |
| _ | Used anywhere in a string to match a single character (only with LIKE or NOT LIKE) 和% 相似，代表1个字符 | col_name LIKE "AN_" (matches "AND", but not "AN") |
| IN (…) | String exists in a list 在列表 | col_name IN ("A", "B", "C") |
| NOT IN (…) | String does not exist in a list 不在列表 | col_name NOT IN ("D", "E", "F") |
3.过滤Filtering、排序sorting、去重distinct
SELECT DISTINCT column, another_column, …
FROM mytable
WHERE condition(s);
SELECT column, another_column, …
FROM mytable
WHERE condition(s)
ORDER BY column ASC/DESC
LIMIT num_limit
OFFSET num_offset;
4.用INNER JOIN 连接表的语法
SELECT column, another_table_column, …
FROM mytable （主表）
INNER/LEFT/RIGHT/FULL JOIN another_table （要连接的表）
ON mytable.id = another_table.id (想象一下刚才讲的主键连接，两个相同的连成1条)
WHERE condition(s)
ORDER BY column, … ASC/DESC
LIMIT num_limit
OFFSET num_offset;最后 LIMIT 和 OFFSET 从排序的结果中截取部分数据.
5.在查询条件中处理 NULL
SELECT column, another_column, …
FROM mytable
WHERE column IS/IS NOT NULL
AND/OR another_condition AND/OR …;
6.包含表达式的例子
SELECT particle_speed / 2.0 AS half_particle_speed (对结果做了一个除2）
FROM physics_data
WHERE ABS(particle_position) * 10.0 >500 （条件要求这个属性绝对值乘以10大于500）;
7.对全部结果数据做统计(函数)
SELECT AGG_FUNC(column_or_expression) AS aggregate_description, …
FROM mytable
WHERE constraint_expression;
下面介绍几个常用统计函数:
| Function | Description |
| COUNT(*), COUNT(column) | 计数！COUNT(*) 统计数据行数，COUNT(column) 统计column非NULL的行数. |
| MIN(column) | 找column最小的一行. |
| MAX(column) | 找column最大的一行. |
| AVG(column) | 对column所有行取平均值. |
| SUM(column) | 对column所有行求和. |
8.用分组的方式统计
SELECT AGG_FUNC(column_or_expression) AS aggregate_description, …
FROM mytable
WHERE constraint_expression
GROUP BY column;
9.用HAVING进行筛选
SELECT group_by_column, AGG_FUNC(column_expression) AS aggregate_result_alias, …
FROM mytable
WHERE condition GROUP BY column
HAVING group_condition;
10.完整的SELECT查询
SELECT DISTINCT column, AGG_FUNC(column_or_expression), …
FROM mytable
JOIN another_table
ON mytable.column = another_table.column
WHERE constraint_expression
GROUP BY column
HAVING constraint_expression
ORDER BY column ASC/DESC
LIMIT count
OFFSET COUNT;