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31 lines
1.7 KiB
SQL
31 lines
1.7 KiB
SQL
SET max_block_size = 10, max_threads = 1;
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-- Take the following example:
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SELECT 1 UNION ALL SELECT 2 FORMAT TSV;
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-- Each subquery can be put in parentheses and have its own settings:
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(SELECT getSetting('max_block_size') SETTINGS max_block_size = 1) UNION ALL (SELECT getSetting('max_block_size') SETTINGS max_block_size = 2) FORMAT TSV;
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-- And the whole query can have settings:
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(SELECT getSetting('max_block_size') SETTINGS max_block_size = 1) UNION ALL (SELECT getSetting('max_block_size') SETTINGS max_block_size = 2) FORMAT TSV SETTINGS max_block_size = 3;
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-- A single query with output is parsed in the same way as the UNION ALL chain:
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SELECT getSetting('max_block_size') SETTINGS max_block_size = 1 FORMAT TSV SETTINGS max_block_size = 3;
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-- So while these forms have a slightly different meaning, they both exist:
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SELECT getSetting('max_block_size') SETTINGS max_block_size = 1 FORMAT TSV;
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SELECT getSetting('max_block_size') FORMAT TSV SETTINGS max_block_size = 3;
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-- And due to this effect, the users expect that the FORMAT and SETTINGS may go in an arbitrary order.
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-- But while this work:
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(SELECT getSetting('max_block_size')) UNION ALL (SELECT getSetting('max_block_size')) FORMAT TSV SETTINGS max_block_size = 3;
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-- This does not work automatically, unless we explicitly allow different orders:
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(SELECT getSetting('max_block_size')) UNION ALL (SELECT getSetting('max_block_size')) SETTINGS max_block_size = 3 FORMAT TSV;
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-- Inevitably, we allow this:
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SELECT getSetting('max_block_size') SETTINGS max_block_size = 1 SETTINGS max_block_size = 3 FORMAT TSV;
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/*^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^*/
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-- Because this part is consumed into ASTSelectWithUnionQuery
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-- and the rest into ASTQueryWithOutput.
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