SELECT
id.id,
id.has_yue_coin AS balance,
id.card_no AS cardNo,
cc.card_name AS cardName,
cc.card_price AS cardPrice,
cv.discount
FROM
issue_detail id
LEFT JOIN card_category cc ON id.card_id = cc.id
LEFT
JOIN card_verification cv ON cc.id = cv.card_id
WHERE
id.member_id =
#{memberId}
<if test="merchantDistrictId != null">
AND (cc.merchant_district_id = #{merchantDistrictId} or
cc.merchant_district_id is null)
</if>
AND cv.merchant_id = #{merchantId}
AND id.`is_expire` = 0
AND
id.issue_status = 1
AND cc.`status` = 0
AND cc.shelf_status = 0
ORDER BY
discount
注意问题如下:
1.字段为null的条件匹配:要用 字段 is null。
2.小括号的优先级问题