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