[求助]如何僅在字段provider_order中刪除NULL值,在我的情況下,表使用JOIN表和UNION

這是我的數(shù)據(jù)庫(kù)模式和我的SQL查詢

為了清楚地描述這里我附上圖片

最佳答案 您不能僅刪除行中的該字段.但是,只需使用WHERE子句過(guò)濾掉具有空值的記錄,就可以擺脫整行.

SELECT

m.provider_id,

m.provider_name,

p.purchase_order_code,

NULL AS purchase_order_sample_code,

p.provider_id AS provider_order

FROM mst_provider AS m

LEFT JOIN trx_purchase_order AS p

ON (m.provider_id = p.provider_id)

WHERE p.provider_id != NULL

UNION

SELECT

m.provider_id,

m.provider_name,

p.purchase_order_code,

NULL AS purchase_order_sample_code,

p.provider_id AS provider_order

FROM mst_provider AS m

RIGHT JOIN trx_purchase_order AS p

ON (m.provider_id = p.provider_id)

UNION

SELECT

m.provider_id,

m.provider_name,

NULL,

s.purchase_order_sample_code,

s.provider_id

FROM mst_provider AS m

RIGHT JOIN trx_purchase_order_sample AS s

ON (s.provider_id = m.provider_id)

總結(jié)

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