adding solutions of the exercises - challenge 2 #49
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juanmdpc
reviewed
Dec 3, 2024
README.md
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| SELECT ac.type, SUM(ac.mount) AS total | ||
| FROM accounts ac | ||
| GROUP BY ac.type; |
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omit using the aliases since we're only using the columns from one table
README.md
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| SELECT ac.id, ac.user_id, ac.type, ac.mount | ||
| FROM accounts ac | ||
| ORDER BY ac.mount DESC | ||
| LIMIT 5; |
README.md
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| WHEN m.type = 'IN' THEN m.mount | ||
| WHEN m.type = 'TRANSFER' AND m.account_to = a.id THEN m.mount | ||
| WHEN m.type = 'TRANSFER' AND m.account_from = a.id THEN -m.mount | ||
| WHEN m.type = 'OUT' THEN -m.mount | ||
| WHEN m.type = 'OTHER' AND m.account_from = a.id THEN -m.mount | ||
| WHEN m.type = 'OTHER' AND m.account_to = a.id THEN m.mount |
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There are two common patterns, so we can reduce these to be 3 conditionals
README.md
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| FROM | ||
| accounts a | ||
| LEFT JOIN | ||
| movements m ON (m.account_from = a.id OR m.account_to = a.id) |
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we can use IN instead of the OR to improve the readibility
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| WHEN m.type = 'IN' THEN m.mount | ||
| WHEN m.type = 'TRANSFER' AND m.account_to = a.id THEN m.mount | ||
| WHEN m.type = 'TRANSFER' AND m.account_from = a.id THEN -m.mount | ||
| WHEN m.type = 'OUT' THEN -m.mount | ||
| WHEN m.type = 'OTHER' AND m.account_from = a.id THEN -m.mount | ||
| WHEN m.type = 'OTHER' AND m.account_to = a.id THEN m.mount |
README.md
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| f. Once the transaction is correct, make a commit | ||
| ``` | ||
| IF saldo_despues_transfer < 731823.56 THEN |
README.md
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| f. Once the transaction is correct, make a commit | ||
| ``` | ||
| IF saldo_despues_transfer < 731823.56 THEN | ||
| RAISE EXCEPTION 'Saldo insuficiente para el movimiento OUT de 731823.56'; |
README.md
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| WHEN m.type = 'IN' THEN m.mount | ||
| WHEN m.type = 'TRANSFER' AND m.account_to = a.id THEN m.mount | ||
| WHEN m.type = 'TRANSFER' AND m.account_from = a.id THEN -m.mount | ||
| WHEN m.type = 'OUT' THEN -m.mount | ||
| WHEN m.type = 'OTHER' AND m.account_from = a.id THEN -m.mount | ||
| WHEN m.type = 'OTHER' AND m.account_to = a.id THEN m.mount |
README.md
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| FROM | ||
| accounts a | ||
| LEFT JOIN | ||
| movements m ON (m.account_from = a.id OR m.account_to = a.id) |
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| us.id AS user_id, | ||
| us.name AS user_name, | ||
| ac.id AS account_id, | ||
| ac.type AS account_type, | ||
| mov.id AS movement_id, | ||
| mov.type AS movement_type, | ||
| mov.mount, | ||
| mov.account_from, | ||
| mov.account_to, | ||
| mov.created_at |
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since we know who is the user we're looking for, we can omit the columns about it, and keep the columns about movements: SELECT mov.*
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