Custom expressions are helpful when the built in operators are not enough. They provide the flexiblity to use SQL expressions & functions to reshape your data.

When you select EXPR it will prompt you to enter a SQL expression. CreateTable.io uses DuckDB (Thanks DuckDB!) under the hood, so you can use any of the duckdb functions in your expression.

Example - Lowercase a column

Let’s say you have a column called name and you want to lowercase it. You can use the LOWER function to do this.

    LOWER(name)

Example - Replace characters in a column

Let’s say you have a column called id and you want to replace all the spaces with underscores. You can use the REPLACE function to do this.

    REPLACE(id, ' ', '_')