Function

DATE_FORMAT

DATE_FORMAT(date,format)

DATE_FORMAT(start_time, '%Y-%m-%d %H:%i:%s')

COALESCE

// 返回第一个非 null 字段
COALESCE(value,...)

DML

检查表是否有数据

SELECT 1 FROM tableA LIMIT 1
SELECT COUNT(*) FROM (SELECT 1 FROM tableA LIMIT 1) t;

关联更新

UPDATE A a INNER JOIN B b ON b.key_id = a.key_id 
SET a.val = 2 WHERE b.satisfy = 1

批量插入查询数据

INSERT INTO tableA(col1, col2, col3)
SELECT col1, col2, col3 FROM tableB

DDL

ALTER TABLE table_name DROP COLUMN column_name;
ALTER TABLE table_name MODIFY COLUMN column_name datatype;
ALTER TABLE tbl_Country CHANGE column_name column_name datatype;

规范

字段统一使用``包住,避免出现与保留关键字冲突

history

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admin cmd

mysql.server start

meta cmd

# 显示表结构
SHOW CREATE TABLE tablename;
DESC tablename;