SQL 二张表数据复制语句

1. sql 子查询应用

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UPDATE hj_cy_jws uset yyid = (            SELECT DISTINCT hj.yyid             FROM hj_cy_jws jw JOIN hj_cy hj ON jw.grid = hj.grid             WHERE u.grid = hj.grid            )WHERE EXISTS (              SELECT * FROM hj_cy_jws jw JOIN hj_cy hj ON jw.grid = hj.grid              WHERE u.grid = hj.grid              )