Structured Query Language（结构化查询语言）
| SQL 语句 | 语法 | 说明 |
|---|---|---|
| AND / OR | SELECT column_name(s) FROM table_name WHERE condition AND|OR condition |
AND：表示逻辑与 OR：表示逻辑或 |
| ALTER TABLE | ALTER TABLE table_name ADD column_name datatype ALTER TABLE table_name DROP COLUMN column_name |
用于修改现有表的结构，添加或删除列。 |
| AS (alias) | SELECT column_name AS column_alias FROM table_name SELECT column_name FROM table_name AS table_alias |
用于为列或表指定别名。 |
| BETWEEN | SELECT column_name(s) FROM table_name WHERE column_name BETWEEN value1 AND value2 | 用于筛选在指定范围内的记录。 |
| CREATE DATABASE | CREATE DATABASE database_name | 用于创建新数据库。 |
| CREATE TABLE | CREATE TABLE table_name (column_name1 data_type, column_name2 data_type, ...) | 用于创建新表，定义表的列和数据类型。 |
| CREATE INDEX | CREATE INDEX index_name ON table_name (column_name) CREATE UNIQUE INDEX index_name ON table_name (column_name) |
用于在表的列上创建索引，以加速查询。 |
| CREATE VIEW | CREATE VIEW view_name AS SELECT column_name(s) FROM table_name WHERE condition | 用于创建视图，以保存复杂查询的结果。 |
| DELETE | DELETE FROM table_name WHERE some_column=some_value DELETE FROM table_name DELETE * FROM table_name |
用于删除表中的记录，DELETE FROM table_name 和 DELETE * FROM table_name 会删除所有记录。 |
| DROP DATABASE | DROP DATABASE database_name | 用于删除数据库。 |
| 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) |
用于删除表上的索引。 |
| DROP TABLE | DROP TABLE table_name | 用于删除表及其所有数据。 |
| GROUP BY | SELECT column_name, aggregate_function(column_name) FROM table_name WHERE column_name operator value GROUP BY column_name | 用于按一个或多个列对结果集进行分组。 |
| 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 | 用于对分组后的结果集进行过滤。 |
| IN | SELECT column_name(s) FROM table_name WHERE column_name IN (value1, value2, ...) | 用于筛选匹配集合中某一值的记录。 |
| INSERT INTO | INSERT INTO table_name VALUES (value1, value2, ...) INSERT INTO table_name (column1, column2, ...) VALUES (value1, value2, ...) |
用于向表中插入新记录。 |
| INNER JOIN | SELECT column_name(s) FROM table_name1 INNER JOIN table_name2 ON table_name1.column_name=table_name2.column_name | 用于返回两个表中匹配的记录。 |
| LEFT JOIN | SELECT column_name(s) FROM table_name1 LEFT JOIN table_name2 ON table_name1.column_name=table_name2.column_name | 用于返回左表中的所有记录和右表中的匹配记录。 |
| RIGHT JOIN | SELECT column_name(s) FROM table_name1 RIGHT JOIN table_name2 ON table_name1.column_name=table_name2.column_name | 用于返回右表中的所有记录和左表中的匹配记录。 |
| FULL JOIN | SELECT column_name(s) FROM table_name1 FULL JOIN table_name2 ON table_name1.column_name=table_name2.column_name | 用于返回两个表中的所有记录，不论是否匹配。 |
| LIKE | SELECT column_name(s) FROM table_name WHERE column_name LIKE pattern | 用于筛选匹配特定模式的记录。 |
| ORDER BY | SELECT column_name(s) FROM table_name ORDER BY column_name [ASC|DESC] |
用于对结果集进行排序。ASC 表示升序排列（默认），DESC 表示降序排列。 |
| SELECT | SELECT column_name(s) FROM table_name | 用于从表中选择数据。 |
| SELECT | SELECT * FROM table_name | 用于选择表中的所有列。 |
| SELECT DISTINCT | SELECT DISTINCT column_name(s) FROM table_name | 用于返回唯一不同的值。 |
| SELECT INTO | SELECT * INTO new_table_name [IN externaldatabase] FROM old_table_name SELECT column_name(s) INTO new_table_name [IN externaldatabase] FROM old_table_name |
用于从一个表中选择数据并插入到新表中。 |
| SELECT TOP | SELECT TOP number|percent column_name(s) FROM table_name ORDER BY column_name [ASC|DESC] |
从表中返回前指定数量的记录，可以指定绝对数量或百分比。 |
| TRUNCATE TABLE | TRUNCATE TABLE table_name | 用于删除表中的所有数据，但不删除表结构。 |
| UNION | SELECT column_name(s) FROM table_name1 UNION SELECT column_name(s) FROM table_name2 | 用于合并两个或多个 SELECT 语句的结果集，不包含重复记录。 |
| UNION ALL | SELECT column_name(s) FROM table_name1 UNION ALL SELECT column_name(s) FROM table_name2 | 用于合并两个或多个 SELECT 语句的结果集，包含重复记录。 |
| UPDATE | UPDATE table_name SET column1=value, column2=value, ... WHERE some_column=some_value | 用于修改表中的现有记录。 |
| WHERE | SELECT column_name(s) FROM table_name WHERE column_name operator value | 用于过滤记录，指定查询条件。 |
