fix(function): fix incorrect return datatype of function if

common/datablocks/src/data_block.rs

@@ -34,6 +34,9 @@ pub struct DataBlock {
 impl DataBlock {
     #[inline]
     pub fn create(schema: DataSchemaRef, columns: Vec<ColumnRef>) -> Self {
+        debug_assert!(
+           schema.fields().iter().zip(columns.iter()).all( |(f, c) | f.data_type() == &c.data_type() );
+        );
         DataBlock { schema, columns }
     }
 

common/functions/src/scalars/conditionals/if.rs

@@ -57,16 +57,18 @@ impl IfFunction {
         &self,
         cond_col: &ColumnRef,
         columns: &ColumnsWithField,
-        _func_ctx: &FunctionContext,
+        func_ctx: &FunctionContext,
     ) -> Result<ColumnRef> {
         debug_assert!(cond_col.is_const());
         // whether nullable or not, we can use viewer to make it
         let cond_viewer = bool::try_create_viewer(cond_col)?;
-        if cond_viewer.value_at(0) {
-            return Ok(columns[0].column().clone());
+        let c = if cond_viewer.value_at(0) {
+            columns[0].clone()
         } else {
-            return Ok(columns[1].column().clone());
-        }
+            columns[1].clone()
+        };
+
+        cast_column_field(&c, c.data_type(), &self.least_supertype, func_ctx)
     }
 
     // lhs is const column and:

tests/suites/0_stateless/02_function/02_0010_function_if.result

@@ -22,3 +22,5 @@ NULL
 NULL
 5
 6
+NULL	0
+0	NULL

tests/suites/0_stateless/02_function/02_0010_function_if.sql

@@ -5,4 +5,8 @@ select if(number>0, 'Z+', 'zero') from numbers(3) order by number;
 select if(number<1, true, null) from numbers(3) order by number;
 select typeof(if(number % 3 = 0, to_uint32(1), to_int64(3))) from numbers(10) limit 1;
 select typeof(if(number % 3 = 0, to_uint32(1), to_float32(3))) from numbers(10) limit 1;
-SELECT if (number % 3 = 1, null, number) as a FROM numbers(7) order by number;
+SELECT if (number % 3 = 1, null, number) as a FROM numbers(7) order by number;
+
+-- constant
+select if(true, null, number), if(false, null, number) from numbers(1);
+select if(true, number, null), if(false, number, null) from numbers(1);