87 lines
1.9 KiB
Markdown
87 lines
1.9 KiB
Markdown
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---
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tags:
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- SQL
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- databases
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---
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# Retrieve data from table with SQL `SELECT` statement
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> Select data from the database. The data returned is stored in a result table
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> called the **result-set**.
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_A table named `models`:_
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| modelId | name | cores | releaseDate |
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| ------- | -------------------- | ----- | ----------- |
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| 2 | Raspberry Pi Model B | 2 | 2022-11-19 |
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| 3 | Raspberry Pi Model C | 4 | 2022-11-25 |
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| 4 | MacBook Pro M2 | 9 | 2022-03-18 |
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## Basic usage
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```sql
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SELECT name FROM models
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```
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We can pass in a comma-separated **list of fields**:
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```sql
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SELECT name, releaseDate FROM models
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```
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## With parameters
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### `WHERE`
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The `WHERE` clause specifies a search criterion. The `WHERE` clause should
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always be last in the syntax. The clauses are always written in this order:
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`FROM` followed by `WHERE`
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```sql
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SELECT name FROM models WHERE cores > 3
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```
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### Compound statements
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Compound statements allow you to apply more filters to your clauses within an
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SQL statement. SQL allows you to build complex, combinatorial `WHERE` clauses by
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using Boolean and mathematical operators (i.e `AND` , `OR` , `>` , `<` , `!=` ,
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`<=` ...)
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Multiple clauses:
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```sql
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SELECT name, ram, release_date
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FROM model
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WHERE release_date > '2018-01-01' AND ram > 512;
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```
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More complex logic achieve with parentheses:
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```sql
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SELECT name, cores, release_date
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FROM model
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WHERE (manufacturer_id = 1 OR manufacturer_id = 2) AND cores >= 2;
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```
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## Transform returned data
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We can apply **ordering** to the return data
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```sql
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SELECT name FROM models ORDER BY name, cores
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SELECT name FROM models ORDER BY name, cores DESC
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```
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> `ORDER BY` always comes last, after the selection and any filtering clauses
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> but _before_ a `WHERE` clause
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## Paginate
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We can break our returned data into blocks with `LIMIT`
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```sql
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LIMIT 5 -- Return first five items
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LIMIT 5,5 -- Return first five items from the sixth row
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```
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