# Queries with Cryptographic Computing for Clean Rooms
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This topic provides information about writing queries that use data tables that have been encrypted using Cryptographic Computing for Clean Rooms.

**Topics**
+ [Queries that branch on NULL](#queries-branch-on-null)
+ [Mapping one source column to multiple target columns](#queries-mapping)
+ [Using the same data for both JOIN and SELECT queries](#queries-using-same-data)

## Queries that branch on NULL
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To have a query branch on a NULL statement means to use syntax like `IF x IS NULL THEN 0 ELSE 1`.

Queries can always branch on NULL statements in cleartext columns. 

Queries can branch on NULL statements in sealed columns and fingerprint columns only when the value of the **Preserve NULL values** parameter (`preserveNulls`) is set to `true`.

Queries that violate these constraints might yield incorrect results.

## Mapping one source column to multiple target columns
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One source column can map to multiple target columns. For example, you might want to both JOIN and SELECT on a column. 

For more information, see [Using the same data for both JOIN and SELECT queries](#queries-using-same-data).

## Using the same data for both JOIN and SELECT queries
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If the data in a column is not sensitive, it can appear in a cleartext target column, which allows it to be used for any purpose.

If data in a column is sensitive and must be used for both JOIN and SELECT queries, map that source column to two target columns in the output file. One column is encrypted with the `type` as a fingerprint column, and one column is encrypted with the `type` as a sealed column. The interactive schema generation of the C3R encryption client suggests header suffixes of `_fingerprint` and `_sealed`. These header suffixes can be a useful convention for differentiating such columns quickly.