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Code Issues Releases Wiki Activity

Fixing PRIMARY_KEY NULL constraint (#4465)

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Akash Sharma
2023-09-12 20:57:19 +05:30
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parent b565ce9bce
commit 79a656e171
1 changed files with 2 additions and 2 deletions
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src/data/roadmaps/sql/content/105-data-constraints/102-unique.md
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@@ -2,7 +2,7 @@
The `UNIQUE` constraint ensures that all values in a column are different; that is, each value in the column should occur only once. The `UNIQUE` constraint ensures that all values in a column are different; that is, each value in the column should occur only once.
Both the `UNIQUE` and `PRIMARY KEY` constraints provide a guarantee for uniqueness for a column or set of columns. However, a primary key can contain only `NULL`, and each table can have only one primary key. On the other hand, a `UNIQUE` constraint allows for one `NULL` value, and a table can have multiple `UNIQUE` constraints. Both the `UNIQUE` and `PRIMARY KEY` constraints provide a guarantee for uniqueness for a column or set of columns. However, a primary key cannot contain `NULL` since it uniquely identifies each row, and each table can have only one primary key. On the other hand, a `UNIQUE` constraint allows for one `NULL` value, and a table can have multiple `UNIQUE` constraints.
## Syntax ## Syntax
```sql ```sql
@@ -51,4 +51,4 @@ ALTER TABLE table_name
DROP CONSTRAINT constraint_name; DROP CONSTRAINT constraint_name;
``` ```
Here, `constraint_name` is the name of the `UNIQUE` constraint that you want to drop. Here, `constraint_name` is the name of the `UNIQUE` constraint that you want to drop.