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  • SQL语法

    1.CREATE
    创建数据库:CREATE DATABASE db_name
    创建表:CREATE TABLE table_name (col_name col_type [NOT NULL] [PRIMARY KEY], ...)

    2.DROP
    删除表:DROP TABLE table_name

    3.ALTER
    添加列:ALTER TABLE table_name ADD COLUMN col_type
    添加主键:ALTER TABLE table_name ADD PRIMARY KEY(col_name)

    4.INSERT
    插入记录:INSERT INTO table_name (col_name, ...) VALUES (col_value, ...)

    5.DELETE
    删除记录:DELETE FROM table_name WHERE col_name=col_value
    *safe update模式只能通过主键字段更新记录,更新同理

    6.UPDATE
    更新记录:UPDATE table_name SET col_name=col_value, ... WHERE ...

    7.SELECT
    查询部分字段:SELECT col_name, ... FROM table_name WHERE ...
    查询全部字段:SELECT * FROM table_name WHERE ...

    8.OUTER JOIN (表)
    table_name1 LEFT/RIGHT OUTER JOIN table_name2
    *左联查询把table1的内容全部查出,table2中只查出满足条件的内容,其他为null

    9.INNER JOIN (表)
    table_name1 INNER JOIN table_name2 ON table_name1.col_name1=table_name2.col_name2
    *只查出满足条件的记录

    10.ORDER BY
    升序:SELECT ... ORDER BY col_name
    降序:SELECT ... ORDER BY col_name DESC

    11.聚合函数(字段)
    和:sum(col_name)
    平均:avg(col_name)
    最大:max(col_name)
    最小:min(col_name)
    计数:count(col_name)

    12.GROUP BY
    某字段同值记录合并:GROUP BY col_name
    eg. SELECT sum(col_name2) as new_col_name FROM table_name GROUP BY col_name

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  • 原文地址:https://www.cnblogs.com/truelycloud/p/10222684.html
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