SQL 语法

SQL是一组语法的独特规则和准则

所有SQL语句都以：SELECT，INSERT，UPDATE，DELETE，ALTER，DROP，CREATE，USE，SHOW等任何关键字开头，所有语句都以分号(;)结尾。

• SQL不区分大小写。通常SQL关键字以大写形式编写。
• SQL语句依赖于文本行，可以在一个或多个文本行上放置一个SQL语句。
• 使用SQL语句可以在数据库中执行大多数操作。
• SQL依赖于关系代数和元组关系演算。

这里要注意的最重要的一点是SQL不区分大小写，所以语句：SELECT和select在SQL语句中具有相同的含义。 然而，MySQL在表名称是区分大小写的。 因此，如果使用MySQL，那么表命名时需要注意。

SQL常用语句语法结构

SQL SELECT语句
SELECT column1, column2....columnN FROM table_name;

SQL DISTINCT子句
SELECT DISTINCT column1, column2....columnN FROM table_name;

SQL WHERE子句
SELECT column1, column2....columnN
FROM table_name WHERE CONDITION;

SQL AND/OR子句
SELECT column1, column2....columnN
FROM table_name WHERE CONDITION-1 {AND|OR} CONDITION-2;

SQL IN子句
SELECT column1, column2....columnN
FROM table_name WHERE column_name IN (val-1, val-2,...val-N);

SQL BETWEEN子句
SELECT column1, column2....columnN
FROM table_name WHERE column_name BETWEEN val-1 AND val-2;

SQL Like子句
SELECT column1, column2....columnN
FROM table_name WHERE column_name LIKE { PATTERN };

SQL ORDER BY子句
SELECT column1, column2....columnN
FROM table_name WHERE CONDITION
ORDER BY column_name {ASC|DESC};

SQL GROUP BY子句
SELECT SUM(column_name)
FROM table_name WHERE CONDITION
GROUP BY column_name;

SQL COUNT子句
SELECT COUNT(column_name)
FROM table_name
WHERE CONDITION;

SQL HAVING子句
SELECT SUM(column_name)
FROM table_name WHERE CONDITION
GROUP BY column_name
HAVING (arithematic function condition);

SQL CREATE TABLE语句
CREATE TABLE table_name(
column1 datatype,
column2 datatype,
column3 datatype,
.....
columnN datatype,
PRIMARY KEY( one or more columns )
);

SQL DROP TABLE语句
DROP TABLE table_name;

SQL CREATE INDEX语句
CREATE UNIQUE INDEX index_name
ON table_name ( column1, column2,...columnN);

SQL DROP INDEX语句
ALTER TABLE table_name
DROP INDEX index_name;

SQL DESC语句
DESC table_name;

SQL TRUNCATE TABLE语句
TRUNCATE TABLE table_name;

SQL ALTER TABLE语句
ALTER TABLE table_name {ADD|DROP|MODIFY} column_name {data_ype};

SQL ALTER TABLE(rename)语句
ALTER TABLE table_name RENAME TO new_table_name;

SQL INSERT INTO语句
INSERT INTO table_name( column1, column2....columnN)
VALUES ( value1, value2....valueN);

SQL UPDATE语句
UPDATE table_name
SET column1 = value1, column2 = value2....columnN=valueN
[ WHERE CONDITION ];

SQL DELETE语句
DELETE FROM table_name WHERE {CONDITION};

SQL CREATE DATABASE语句
CREATE DATABASE database_name;

SQL DROP DATABASE语句
DROP DATABASE database_name;

SQL USE语句
USE database_name;

SQL COMMIT语句
COMMIT;

SQL ROLLBACK语句
ROLLBACK;