[英]How can I add a where clause to a right outer join union left outer join?
[英]How can I convert a NOT IN Clause into a left outer join in MySQL
我試圖將查詢從NOT IS子句轉換為左外連接以獲得更好的性能。
以下是我的查詢完美
SELECT a.company_code, account_name, legal_name FROM accounts a
WHERE account_id NOT IN (SELECT DISTINCT account_id FROM phone_calls WHERE status = 2 ) AND account_id >10000
ORDER BY legal_name, account_name, account_id
所以我想將它更改為左連接或某些類型的連接,它們將執行相同的查詢。 我試過這個,但它不適合我
SELECT a.company_code, a.account_name, a.legal_name, p.phone_call_id
FROM accounts AS a
LEFT JOIN phone_calls AS p ON p.account_id = a.account_id
WHERE a.account_id >= 10000 AND p.status = 2 AND p.phone_call_id IS NULL
ORDER BY a.legal_name, a.account_name, a.account_id
我的第二個查詢總是沒有返回。
我試過這個查詢,這給了我更多的結果,第一個查詢所以它不一樣
SELECT a.company_code, a.account_name, a.legal_name, p.phone_call_id
FROM accounts AS a
LEFT JOIN phone_calls AS p ON p.account_id = a.account_id AND p.status = 2 AND a.account_id >= 10000
WHERE p.account_id IS NULL
ORDER BY a.legal_name, a.account_name, a.account_id
在join
子句中檢查p.status = 2
,而不是在where
子句中:
SELECT a.company_code, a.account_name, a.legal_name, p.phone_call_id
FROM accounts AS a
LEFT JOIN phone_calls AS p ON p.account_id = a.account_id AND p.status = 2
WHERE a.account_id >= 10000
AND p.phone_call_id IS NULL
ORDER BY a.legal_name, a.account_name, a.account_id
如果你將它放在where子句中,phone_calls將被加入,你將在加入后進行檢查
這些陳述可能完全沖突(所有帶狀態= 2的phone_calls都有一個id)。
一般來說,你不應該在WHERE子句中加入一個左連接子句( IS NULL
/ IS NOT NULL
除外)
只是好奇,但嘗試使用NOT EXISTS
子句:
SELECT company_code
, account_name
, legal_name
FROM accounts a
WHERE account_id > 10000
AND NOT EXISTS (
SELECT 1
FROM phone_calls b
WHERE b.status = 2
AND b.account_id = a.account_id
)
ORDER BY legal_name, account_name, account_id
我認為只有一個EXPLAIN
才能揭示哪種技術更好。 通過未選擇的列對結果進行排序似乎很奇怪,但這是一個不同的問題。
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.