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sql subquery where

Innocent Iguana answered on January 19, 2024 Popularity 8/10 Helpfulness 4/10

answer sql subquery where

sql subquery where

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-- Simple query with two tables
SELECT left_table.colx, right_table.coly
FROM left_table, right_table
WHERE left_table.common_col = right_table.common_col

-- Subquery inside FROM (turning a query into virtual table using alias, evolving from the previous query)
SELECT left_table.colx, right_table.coly
FROM left_table,
    (SELECT coly, colz, common_col          -- subquery start
    FROM another_table) AS right_table      -- subquery end
WHERE left_table.common_col = right_table.common_col
ORDER BY continent;


-- Subquery inside WHERE (You use it in Semi join / Anti Join)
SELECT left_table.*
FROM left_table
WHERE left_table.some_col <NOT> IN  -- Using "NOT" will result in Anti join
        (                           -- subquery start
            SELECT another_col      
            FROM right_table
        );                          -- subquery end

-- Subquery inside SELECT
SELECT
    outer_table.id,
    (SELECT COUNT(*) FROM inner_table WHERE outer_table.id = inner_table.id) AS new_col_1,              -- subquery 1
    (SELECT AVG(some_column) FROM inner_table WHERE outer_table.id = inner_table.id) AS new_col_2,      -- subquery 2
    (SELECT MAX(another_column) FROM inner_table WHERE outer_table.id = inner_table.id) AS new_col_3    -- subquery 3
FROM
    outer_table;

-- Using the WITH keyword (creating multiple virtual tables)
WITH
result_table1 AS (
    SELECT col1, col2 FROM t1),             -- subquery 1
result_table2 AS (
    SELECT colx, coly FROM t2)              -- subquery 2
SELECT * FROM result_table1, result_table2
WHERE result_table1.col1 <= result_table2.col2

Popularity 8/10 Helpfulness 4/10 Language sql

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Contributed on Jan 19 2024

Innocent Iguana

0 Answers Avg Quality 2/10

sql subquery where

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