SQL在這兩個語句之間的性能有差異嗎？ SELECT distinct 'A' as TableName, Col1, Col2, Col3 FROM A
UNION ALL
SELECT distinct 'B' as TableName, Col1, Col2, Col3 from B
與 SELECT 'A' as TableName, Col1, Col2, Col3 FROM A
這裏是我的查詢， SELECT si.* FROM
FROM SHIPMENT_ITEMS si
WHERE ID IN (SELECT ID FROM id_map WHERE code = 'A')
AND LAST_UPDATED BETWEEN TO_DATE('20150102','YYYYMMDD') - 1 AND TO_DATE('20150103','YYYYMMD
在MySQL select various(functions(here(...))) foo, count(*) ct
from table
group by foo
having ct > 1;
看起來重複數據刪除一切，我有一個查詢。我想更改查詢以從foo刪除加號和其後的任何內容，以便如果various(functions(here(...)))得到foo+bar我只得到foo。 （