当列不为空时的sql大小写

Question

我之前问了一个类似的问题，回去重新审视我的逻辑。这是最新消息。我在teamsql中运行mysql。

我想限制当一个列(lc.ladder_advocacy)不为空时的情况。

SELECT 
@row_number:=(CASE
    WHEN @member_id = lh.member_id and lc.ladder_advocacy IS NOT NULL 
THEN @row_number + 1
    ELSE 1
END) AS rank,
@member_id:=lh.member_id AS member_id,
lc.name,
lh.trigger_event_date,
lc.ladder_advocacy 
FROM
leenk_ladder_history AS lh
LEFT JOIN leeds_so.leenk_ladder_config AS lc ON lh.ladder_config_id = lc.id
WHERE
ladder_change = 1 AND trigger_active = 1 
ORDER BY member_id , trigger_event_date DESC;

我也尝试过：

lc.ladder_advocacy <> ``
lc.ladder_advocacy <> ""
lc.ladder_advocacy != ""
lc.ladder_advocacy != ``

在lc.ladder_advocacy列显示空值的情况下，仍然得到返回结果。

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有什么想法吗？