
```sql
alter table users alter column email drop not null;
```


How to Remove a Not Null Constraint

How to Create an Index

How to Compare Arrays

How to Concatenate Strings

How to Convert the Case of a String

How to Create an Array

How to Exclude Current or Partial Weeks

How to Insert Data Into an Array

How to Modify Arrays

How to Query Arrays

How to Replace Substrings

How to Trim Strings

How to Use BETWEEN Correctly

How to Use Lateral Joins

How to Use nullif()

How to Use string_agg()

How to Use substring()

How to Use substring() with Regular Expressions

How to Insert

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How to Delete

How to Create a Table

How to Drop a Table

How to Rename a Table

How to Truncate a Table

How to Duplicate a Table

How to Add a Column

How to Drop a Column

How to Rename a Column

How to Add a Default Value to a Column

How to Remove a Default Value From a Column

How to Add a Not Null Constraint

How to Drop an Index

How to Create a View

How to Drop a View

How to Alter Sequence

How to Query Date and Time

How to Group by Time

How to Round Timestamps

How to Convert UTC to Local Time Zone

How to Calculate Percentiles

How to Get the First Row per Group

How to Use generate_series to Avoid Gaps In Data

How to Do Type Casting

How to Write a Common Table Expression

How to Import a CSV

How to Compare Two Values When One Is Null

How to Use Coalesce

How to Write a Case Statement

How to Query a JSON Column

How to Use Filter to Have Multiple Counts

How to Calculate Cumulative Sum-Running Total

How to Use DISTKEY, SORTKEY and Define Column Compression Encoding

How to Add or Remove Default Values or Null Constraints to a Column

How to Avoid Gaps in Data

How to Compare Two Values When One is Null

How to Have Multiple Counts

How to Remove a Default Value to a Column

How to Remove a Not Null Constraint in PostgreSQL

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