> For the complete documentation index, see [llms.txt](https://mariadb.com/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mariadb.com/docs/server/reference/error-codes/mariadb-error-codes-1900-to-1999/e1923.md).

# Error 1923: At least one of the 'in\_to\_exists' or 'materialization' optimizer\_switch flags must be '

| Error Code | SQLSTATE | Error                                      | Description                                                                                     |
| ---------- | -------- | ------------------------------------------ | ----------------------------------------------------------------------------------------------- |
| 1923       |          | ER\_ILLEGAL\_SUBQUERY\_OPTIMIZER\_SWITCHES | At least one of the 'in\_to\_exists' or 'materialization' optimizer\_switch flags must be 'on'. |

## Possible Causes and Solutions

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