運行Postres 7.4(是升級)複雜的查詢優化
這是一個視圖的查詢和它的使用了很多,但需要更長的時間比我想的。任何優化建議?隨着名稱的ID的任何字段建立索引
SELECT
db_tbl_1.field_id, s."Field ID" AS foreign_field_id,
s."Field Name" AS field_name,
CASE
WHEN SUBSTRING(s."Field ID" FROM 0 FOR 3) = '01' THEN 'Field Label 1'
WHEN SUBSTRING(s."Field ID" FROM 0 FOR 4) = '321' THEN 'Field Label 1'
WHEN SUBSTRING(s."Field ID" FROM 0 FOR 5) = '1234' THEN 'Field Label 1'
WHEN SUBSTRING(s."Field ID" FROM 0 FOR 6) = '55555' THEN 'Field Label 1'
WHEN SUBSTRING(s."Field ID" FROM 0 FOR 3) = '76' THEN 'Field Label 2'
END AS new_field, s.field_1,
db_tbl_2.field_2, db_tbl_1.field_2_a,
db_tbl_1.field_3, db_tbl_1.field_4,
db_tbl_1.field_5, db_tbl_1.field_6, db_tbl_1.field_date_1,
db_tbl_1.field_7, db_tbl_2.field_8 AS new_field_name,
s."Field Date" AS field_date, db_tbl_1.created_date,
CASE
WHEN (((DATE_TRUNC('month', "Field Date") + INTERVAL '2 MONTH') - "Field Date" > 60) AND
((DATE_TRUNC('month', "Field Date") + INTERVAL '2 MONTH') - "Field Date" <= 92))
THEN (DATE_TRUNC('month', "Field Date") + INTERVAL '2 MONTH')
-- the most days in a three month span can be 92
ELSE (DATE_TRUNC('month', "Field Date") + INTERVAL '3 MONTH')
END AS next_date
FROM db_schema_1.db_tbl_1, db_schema_1.db_tbl_2, "Table S" AS s
WHERE db_tbl_1.program_level_id = db_tbl_2.id
AND db_tbl_1.field_id = s."Another ID"
AND (CASE
WHEN SUBSTRING(s."Field ID" FROM 0 FOR 3) = '01' THEN 1
WHEN SUBSTRING(s."Field ID" FROM 0 FOR 4) = '321' THEN 1
WHEN SUBSTRING(s."Field ID" FROM 0 FOR 5) = '1234' THEN 1
WHEN SUBSTRING(s."Field ID" FROM 0 FOR 6) = '55555' THEN 1
WHEN SUBSTRING(s."Field ID" FROM 0 FOR 3) = '76' THEN 1
ELSE 0
END) = 1
不張貼作爲一個答案,因爲我不知道的Postgres,但在SQL Server中我儘量避免'SUBSTRING',而是在這樣的情況下使用'LEFT',因爲'LEFT'將使用索引和'SUBSTRING '不會。爲了得到那個'SUBSTRING',它可能評估每一行,並且只是做一個表掃描。 – JNK
嗯,沒有找到與Postgres 7.4,或任何Postgres版本的LEFT()的文檔。你能提供一個參考嗎? –
它顯然不在那裏!告訴你我不知道Postgres :) – JNK