1,mysql

concat('a','b','c')和concat_ws('a','b','c')的區別:前者如果有某個值為空,結果為空;後者如果有某個值為空,可以忽略這個控制

SELECT
    concat_ws('',FORE_TWO,THIRD_POSITION,FOURTH_POSITION,FIFTH_POSITION) AS code
    FROM
      TABLE_A
    WHERE
      ID= #{id}

2,oracle

SELECT
    FORE_TWO||THIRD_POSITION||FOURTH_POSITION||FIFTH_POSITION AS code
    FROM
      TABLE_A
    WHERE
      ID = #{id}