Add coalesce node support for computed columns (babelfish-for-postgresql#3552)

We invoke sys.tsql_get_expr function for getting the column definition in sys.computed_columns. At present tsql_get_expr function doesn't support Coalesce type in computed columns and return null when we try to obtain computed column expression containing Coalesce expression. Adding support for Coalesce node types for computed column expressions.

Task: Babel-5460

Signed-off-by: Sharath BP <sharatbp@amazon.com>
(cherry picked from commit ad1d762)

Author: sharathbp

contrib/babelfishpg_tsql/src/pltsql_ruleutils.c

@@ -1449,7 +1449,17 @@ get_rule_expr(Node *node, deparse_context *context,
 					appendStringInfoChar(buf, ')');
 			}
 			break;
+		
+		case T_CoalesceExpr:
+			{
+				CoalesceExpr *coalesceexpr = (CoalesceExpr *) node;
 
+				appendStringInfoString(buf, "COALESCE(");
+				get_rule_expr((Node *) coalesceexpr->args, context, true);
+				appendStringInfoChar(buf, ')');
+			}
+			break;
+		
 		case T_SetToDefault:
 			appendStringInfoString(buf, "DEFAULT");
 			break;

test/JDBC/expected/sys-computed_columns-vu-prepare.out

@@ -4,6 +4,7 @@ GO
 CREATE TABLE sys_computed_columns_vu_prepare_t1 ( 
   scc_first_number smallint,
   scc_second_number money,
-  scc_multiplied AS scc_first_number * scc_second_number
+  scc_multiplied AS scc_first_number * scc_second_number,
+  scc_coalesce_col AS COALESCE(scc_first_number, 10) PERSISTED
 )
 GO

test/JDBC/expected/sys-computed_columns-vu-verify.out

@@ -25,11 +25,12 @@ scc_multiplied#!#(scc_first_number * scc_second_number)
 ~~END~~
 
 
-Select sys.tsql_get_expr(adbin, adrelid) FROM pg_attrdef WHERE adrelid = (select oid from pg_class where relname='sys_computed_columns_vu_prepare_t1')
+Select sys.tsql_get_expr(adbin, adrelid) as text FROM pg_attrdef WHERE adrelid = (select oid from pg_class where relname='sys_computed_columns_vu_prepare_t1') ORDER BY text
 GO
 ~~START~~
 text
 (scc_first_number * scc_second_number)
+COALESCE(CAST((scc_first_number) AS int), 10)
 ~~END~~
 
 
@@ -64,3 +65,4 @@ text
 <NULL>
 ~~END~~
 
+

test/JDBC/input/views/sys-computed_columns-vu-prepare.sql

@@ -4,6 +4,7 @@ GO
 CREATE TABLE sys_computed_columns_vu_prepare_t1 ( 
   scc_first_number smallint,
   scc_second_number money,
-  scc_multiplied AS scc_first_number * scc_second_number
+  scc_multiplied AS scc_first_number * scc_second_number,
+  scc_coalesce_col AS COALESCE(scc_first_number, 10) PERSISTED
 )
 GO

test/JDBC/input/views/sys-computed_columns-vu-verify.sql

@@ -10,7 +10,7 @@ WHERE name in ('scc_first_number', 'scc_second_number', 'scc_multiplied')
 ORDER BY name
 GO
 
-Select sys.tsql_get_expr(adbin, adrelid) FROM pg_attrdef WHERE adrelid = (select oid from pg_class where relname='sys_computed_columns_vu_prepare_t1')
+Select sys.tsql_get_expr(adbin, adrelid) as text FROM pg_attrdef WHERE adrelid = (select oid from pg_class where relname='sys_computed_columns_vu_prepare_t1') ORDER BY text
 GO
 
 Select sys.tsql_get_expr('scc_second_number',123)
@@ -23,4 +23,5 @@ Select sys.tsql_get_expr('abc',0)
 GO
 
 Select sys.tsql_get_expr(null, null)
-GO
+GO
+