MySQL concat函数是数据库中众多的函数之一,下文将对MySQL concat函数的语法和使用进行说明,供您参考和学习。
MySQL concat函数使用方法:
CONCAT(str1,str2,…)返回结果为连接参数产生的字符串。如有任何一个参数为NULL ,则返回值为 NULL。
注意:
如果所有参数均为非二进制字符串,则结果为非二进制字符串。 如果自变量中含有任一二进制字符串,则结果为一个二进制字符串。一个数字参数被转化为与之相等的二进制字符串格式;若要避免这种情况,可使用显式类型 cast, 例如:SELECT CONCAT(CAST(int_col AS CHAR), char_col)MySQL concat函数可以连接一个或者多个字符串,如
- mysql> select concat('10');
- +--------------+
- | concat('10') |
- +--------------+
- | 10 |
- +--------------+
- 1 row in set (0.00 sec)
- mysql> select concat('11','22','33');
- +------------------------+
- | concat('11','22','33') |
- +------------------------+
- | 112233 |
- +------------------------+
- 1 row in set (0.00 sec)
MySQL的concat函数在连接字符串的时候,只要其中一个是NULL,那么将返回NULL
-
- mysql> select concat('11','22',null);
- +------------------------+
- | concat('11','22',null) |
- +------------------------+
- | NULL |
- +------------------------+
- 1 row in set (0.00 sec)
- =====================================================================================
- 例子mybatis:
- <select id="loadImgAdP" parameterType="map" resultType="map">
-
select ac.company, date_format(avd.`timeDate`, '%Y-%m-%d') timeDate, ar.des, avd.playDay, ad.title, concat(v.cityName, '-', v.countyName, '-', v.streetName, '-', v.villageName) vname from ad_village_day avd, advert ad, village v, advert_rule ar, ad_company ac WHERE avd.aid = ad.id AND avd.vid = v.id AND ad.rid = ar.id AND ac.id = ad.cid <if test="cid != null and cid != ''"> AND ac.id = #{cid} </if> <if test="cname != null and cname != ''"> AND ac.company like concat('%',#{cname},'%') </if> <if test="villageName != null and villageName != ''"> AND v.villageName like concat('%',#{vname},'%') </if> <if test="atitle != null and atitle != ''"> AND ad.title like concat('%',#{atitle},'%') </if> <if test="startTime != null and startTime != ''"> <![CDATA[ AND date_format(avd.`timeDate`, '%Y%m%d') >= date_format(#{startTime}, '%Y%m%d') ]]> </if> <if test="endTime != null and endTime != ''"> <![CDATA[ AND date_format(avd.`timeDate`, '%Y%m%d') <= date_format(#{endTime}, '%Y%m%d') ]]> </if> ORDER BY avd.aid desc ,avd.timeDate, vname limit #{pageNo}, #{pageSize} </select>