51 lines
922 B
Markdown
51 lines
922 B
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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# Useful operators in SQL
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## True and false
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> In SQL false results are represented by `0` and true results are represented
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> by `1`. Any zero value is false and any non-zero value is true.
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> When comparing operators we can use `SELECT` as a general "execute" function
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> for SQL to interpret
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```sql
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SELECT 0 = 0 -- 1
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SELECT 0.0 = 0 -- 1
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SELECT 9 >= 12 -- 0
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```
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## Boolean operators
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SQL supports all Boolean operators:
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```sql
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SELECT (9 > 7) AND (3 < 5) -- 1
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SELECT (3 > 1) OR (2 > 5) -- 1
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SELECT (3 > 1) XOR (5 > 1) -- 0
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```
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We also have `IS` and `IS NOT` for testing Boolean values:
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```sql
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SELECT (9 > 7) IS TRUE -- 1
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SELECT (9 > 7) IS NOT TRUE -- 0
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```
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## `NULL`
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- `NULL` is neither true (1) or false (0). It has no value.
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- An empty string (`""`) is **not** `NULL`
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```sql
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SELECT 1 IS NULL -- 0
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SELECT 1 IS NOT NULL -- 1
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SELECT NULL IS NULL -- 1
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SELECT "" IS NULL -- 0
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```
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