SQL 快速参考
| SQL 语句 | 语法 |
|---|---|
| AND / OR | SELECT column_name(s) FROM table_name WHERE condition AND|OR condition |
| ALTER TABLE | ALTER TABLE table_name ADD column_name datatype or ALTER TABLE table_name |
| AS (alias) | SELECT column_name AS column_alias FROM table_name or SELECT column_name |
| BETWEEN | SELECT column_name(s) FROM table_name WHERE column_name BETWEEN value1 AND value2 |
| CREATE DATABASE | CREATE DATABASE database_name |
| CREATE TABLE | CREATE TABLE table_name ( column_name1 data_type, column_name2 data_type, column_name2 data_type, ... ) |
| CREATE INDEX | CREATE INDEX index_name ON table_name (column_name) or CREATE UNIQUE INDEX index_name |
| CREATE VIEW | CREATE VIEW view_name AS SELECT column_name(s) FROM table_name WHERE condition |
| DELETE | DELETE FROM table_name WHERE some_column=some_value or DELETE FROM table_name DELETE * FROM table_name |
| DROP DATABASE | DROP DATABASE database_name |
| DROP INDEX | DROP INDEX table_name.index_name (SQL Server) DROP INDEX index_name ON table_name (MS Access) DROP INDEX index_name (DB2/Oracle) ALTER TABLE table_name DROP INDEX index_name (MySQL) |
| DROP TABLE | DROP TABLE table_name |
| GROUP BY | SELECT column_name, aggregate_function(column_name) FROM table_name WHERE column_name operator value GROUP BY column_name |
| HAVING | SELECT column_name, aggregate_function(column_name) FROM table_name WHERE column_name operator value GROUP BY column_name HAVING aggregate_function(column_name) operator value |
| IN | SELECT column_name(s) FROM table_name WHERE column_name IN (value1,value2,..) |
| INSERT INTO | INSERT INTO table_name VALUES (value1, value2, value3,....) or INSERT INTO table_name |
| INNER JOIN | SELECT column_name(s) FROM table_name1 INNER JOIN table_name2 ON table_name1.column_name=table_name2.column_name |
| LEFT JOIN | SELECT column_name(s) FROM table_name1 LEFT JOIN table_name2 ON table_name1.column_name=table_name2.column_name |
| RIGHT JOIN | SELECT column_name(s) FROM table_name1 RIGHT JOIN table_name2 ON table_name1.column_name=table_name2.column_name |
| FULL JOIN | SELECT column_name(s) FROM table_name1 FULL JOIN table_name2 ON table_name1.column_name=table_name2.column_name |
| LIKE | SELECT column_name(s) FROM table_name WHERE column_name LIKE pattern |
| ORDER BY | SELECT column_name(s) FROM table_name ORDER BY column_name [ASC|DESC] |
| SELECT | SELECT column_name(s) FROM table_name |
| SELECT * | SELECT * FROM table_name |
| SELECT DISTINCT | SELECT DISTINCT column_name(s) FROM table_name |
| SELECT INTO | SELECT * INTO new_table_name [IN externaldatabase] FROM old_table_name or SELECT column_name(s) |
| SELECT TOP | SELECT TOP number|percent column_name(s) FROM table_name |
| TRUNCATE TABLE | TRUNCATE TABLE table_name |
| UNION | SELECT column_name(s) FROM table_name1 UNION SELECT column_name(s) FROM table_name2 |
| UNION ALL | SELECT column_name(s) FROM table_name1 UNION ALL SELECT column_name(s) FROM table_name2 |
| UPDATE | UPDATE table_name SET column1=value, column2=value,... WHERE some_column=some_value |
| WHERE | SELECT column_name(s) FROM table_name WHERE column_name operator value |
SQL 函数
SQL 拥有很多可用于计数和计算的内建函数。
SQL Aggregate 函数
SQL Aggregate 函数计算从列中取得的值，返回一个单一的值。
有用的 Aggregate 函数：
- AVG() - 返回平均值
- COUNT() - 返回行数
- FIRST() - 返回第一个记录的值
- LAST() - 返回最后一个记录的值
- MAX() - 返回最大值
- MIN() - 返回最小值
- SUM() - 返回总和
SQL Scalar 函数
SQL Scalar 函数基于输入值，返回一个单一的值。
有用的 Scalar 函数：
- UCASE() - 将某个字段转换为大写
- LCASE() - 将某个字段转换为小写
- MID() - 从某个文本字段提取字符，MySql 中使用
- SubString(字段，1，end) - 从某个文本字段提取字符
- LEN() - 返回某个文本字段的长度
- ROUND() - 对某个数值字段进行指定小数位数的四舍五入
- NOW() - 返回当前的系统日期和时间
- FORMAT() - 格式化某个字段的显示方式