chore: Migrate coalesce_op operator to SQLGlot

bigframes/core/compile/sqlglot/expressions/generic_ops.py

@@ -24,6 +24,7 @@
 import bigframes.core.compile.sqlglot.scalar_compiler as scalar_compiler
 
 register_unary_op = scalar_compiler.scalar_op_compiler.register_unary_op
+register_binary_op = scalar_compiler.scalar_op_compiler.register_binary_op
 register_nary_op = scalar_compiler.scalar_op_compiler.register_nary_op
 register_ternary_op = scalar_compiler.scalar_op_compiler.register_ternary_op
 
@@ -159,6 +160,13 @@ def _(*cases_and_outputs: TypedExpr) -> sge.Expression:
     )
 
 
+@register_binary_op(ops.coalesce_op)
+def _(left: TypedExpr, right: TypedExpr) -> sge.Expression:
+    if left.expr == right.expr:
+        return left.expr
+    return sge.Coalesce(this=left.expr, expressions=[right.expr])
+
+
 @register_nary_op(ops.RowKey)
 def _(*values: TypedExpr) -> sge.Expression:
     # All inputs into hash must be non-null or resulting hash will be null

tests/unit/core/compile/sqlglot/expressions/snapshots/test_generic_ops/test_coalesce/out.sql

@@ -0,0 +1,16 @@
+WITH `bfcte_0` AS (
+  SELECT
+    `int64_col` AS `bfcol_0`,
+    `int64_too` AS `bfcol_1`
+  FROM `bigframes-dev`.`sqlglot_test`.`scalar_types`
+), `bfcte_1` AS (
+  SELECT
+    *,
+    `bfcol_0` AS `bfcol_2`,
+    COALESCE(`bfcol_1`, `bfcol_0`) AS `bfcol_3`
+  FROM `bfcte_0`
+)
+SELECT
+  `bfcol_2` AS `int64_col`,
+  `bfcol_3` AS `int64_too`
+FROM `bfcte_1`

tests/unit/core/compile/sqlglot/expressions/test_generic_ops.py

@@ -209,6 +209,20 @@ def test_case_when_op(scalar_types_df: bpd.DataFrame, snapshot):
     snapshot.assert_match(sql, "out.sql")
 
 
+def test_coalesce(scalar_types_df: bpd.DataFrame, snapshot):
+    bf_df = scalar_types_df[["int64_col", "int64_too"]]
+
+    sql = utils._apply_ops_to_sql(
+        bf_df,
+        [
+            ops.coalesce_op.as_expr("int64_col", "int64_col"),
+            ops.coalesce_op.as_expr("int64_too", "int64_col"),
+        ],
+        ["int64_col", "int64_too"],
+    )
+    snapshot.assert_match(sql, "out.sql")
+
+
 def test_clip(scalar_types_df: bpd.DataFrame, snapshot):
     op_expr = ops.clip_op.as_expr("rowindex", "int64_col", "int64_too")