[b/330573524] Prevent IF from treating NULL as FALSE

Tableau offers the IIF function with the signature IIF(bool, val1, val2[, val3]). If bool is TRUE, it returns val1, if it is FALSE, it returns val2, and if it is NULL, it returns val3 if provided, otherwise it returns NULL. Previously, we translated this behavior by rewriting it as BigQuery's IF. The issue however, is that if bool is NULL, BigQuery defaults to val2 instead of NULL or val3. This commit corrects for that by wrapping the expression in another IF that checks if bool is NULL. If it is, it returns val3 if specified, otherwise NULL. If bool is not null, it follows normal IF behavior.
tanclary · Mar 27, 2024 · 18117bb · 18117bb
1 parent b90add5
commit 18117bb
Showing 1 changed file with 7 additions and 6 deletions.
diff --git a/connector/tableau/looker-jdbc/dialect.tdd b/connector/tableau/looker-jdbc/dialect.tdd
@@ -667,7 +667,8 @@
       <argument type='spatial' />
     </function>
     <function group='logical' name='IIF' return-type='bool'>
-      <formula>IF((%1), (%2), (%3))</formula>
+      <!-- To prevent IF from coercing NULL to FALSE, wrap in another IF that checks for NULL. -->
+      <formula>IF((%1) IS NOT NULL, IF((%1), (%2), (%3)), NULL)</formula>
       <argument type='bool' />
       <argument type='bool' />
       <argument type='bool' />
@@ -687,7 +688,7 @@
       <argument type='real' />
     </function>
     <function group='logical' name='IIF' return-type='int'>
-      <formula>IF((%1), (%2), (%3))</formula>
+      <formula>IF((%1) IS NOT NULL, IF((%1), (%2), (%3)), NULL)</formula>
       <argument type='bool' />
       <argument type='int' />
       <argument type='int' />
@@ -700,7 +701,7 @@
       <argument type='int' />
     </function>
     <function group='logical' name='IIF' return-type='str'>
-      <formula>IF((%1), (%2), (%3))</formula>
+      <formula>IF((%1) IS NOT NULL, IF((%1), (%2), (%3)), NULL)</formula>
       <argument type='bool' />
       <argument type='str' />
       <argument type='str' />
@@ -713,7 +714,7 @@
       <argument type='str' />
     </function>
     <function group='logical' name='IIF' return-type='datetime'>
-      <formula>IF((%1), (%2), (%3))</formula>
+      <formula>IF((%1) IS NOT NULL, IF((%1), (%2), (%3)), NULL)</formula>
       <argument type='bool' />
       <argument type='datetime' />
       <argument type='datetime' />
@@ -726,7 +727,7 @@
       <argument type='datetime' />
     </function>
     <function group='logical' name='IIF' return-type='date'>
-      <formula>IF((%1), (%2), (%3))</formula>
+      <formula>IF((%1) IS NOT NULL, IF((%1), (%2), (%3)), NULL)</formula>
       <argument type='bool' />
       <argument type='date' />
       <argument type='date' />
@@ -739,7 +740,7 @@
       <argument type='date' />
     </function>
     <function group='logical' name='IIF' return-type='spatial'>
-      <formula>IF((%1), (%2), (%3))</formula>
+      <formula>IF((%1) IS NOT NULL, IF((%1), (%2), (%3)), NULL)</formula>
       <argument type='bool' />
       <argument type='spatial' />
       <argument type='spatial' />