fix: CAST(x AS CHAR) not supported by MySQL below v4.0.2

Refs #2531

Author: ansgarbecker

source/dbconnection.pas

@@ -10986,26 +10986,28 @@ procedure TTableColumn.ParseDatatype(Source: String);
 
 
 function TTableColumn.CastAsText: String;
+var
+  ColTypeAllowsCast: Boolean;
 begin
   // Cast data types which are incompatible to string functions to text columns
   Result := FConnection.QuoteIdent(Name);
+  ColTypeAllowsCast := True;
   case FConnection.Parameters.NetTypeGroup of
     ngMySQL, ngSQLite: begin
-      if DataType.Index in [dbdtUnknown, dbdtDate, dbdtDatetime, dbdtTime, dbdtTimestamp, dbdtJson, dbdtJsonB] then
-        Result := 'CAST('+Result+' AS CHAR)';
+      ColTypeAllowsCast := DataType.Index in [dbdtUnknown, dbdtDate, dbdtDatetime, dbdtTime, dbdtTimestamp, dbdtJson, dbdtJsonB];
     end;
     ngMSSQL: begin
       // Be sure LEFT() and "col LIKE xyz" work with MSSQL
       // Also, prevent exceeding size limit of 8000 for NVARCHAR
-      if DataType.Index in [dbdtUnknown, dbdtNtext, dbdtText] then
-        Result := 'CAST('+Result+' AS NVARCHAR('+IntToStr(GRIDMAXDATA)+'))';
+      ColTypeAllowsCast := DataType.Index in [dbdtUnknown, dbdtNtext, dbdtText];
     end;
     ngPgSQL: begin
       // Cast most datatypes, including VARCHAR and TEXT, which may have an [] array attribute
-      if not (DataType.Category in [dtcInteger, dtcReal]) then
-        Result := Result + '::text';
+      ColTypeAllowsCast := not (DataType.Category in [dtcInteger, dtcReal]);
     end;
   end;
+  if ColTypeAllowsCast and FConnection.SqlProvider.Has(qCastAsText) then
+    Result := FConnection.SqlProvider.GetSql(qCastAsText, [Result]);
 end;
 
 

source/dbstructures.interbase.pas

@@ -234,6 +234,7 @@ function TInterbaseProvider.GetSql(AId: TQueryId): string;
       '   RDB$CHARACTER_SET_ID'+
       ' FROM RDB$COLLATIONS';
     qGetCharsets: Result := 'SELECT RDB$CHARACTER_SET_NAME AS "Charset", RDB$CHARACTER_SET_NAME AS "Description" FROM RDB$CHARACTER_SETS';
+    else Result := inherited;
   end;
 end;
 

source/dbstructures.mssql.pas

@@ -3,7 +3,7 @@
 interface
 
 uses
-  dbstructures, StrUtils;
+  dbstructures, StrUtils, SysUtils;
 
 type
   TMsSqlProvider = class(TSqlProvider)
@@ -413,6 +413,7 @@   TMsSqlProvider = class(TSqlProvider)
 
 implementation
 
+{$I const.inc}
 
 function TMsSqlProvider.GetSql(AId: TQueryId): string;
 begin
@@ -480,6 +481,7 @@ function TMsSqlProvider.GetSql(AId: TQueryId): string;
       'SELECT SUM("rows") FROM "sys"."partitions" WHERE "index_id" IN (0, 1) AND "object_id" = object_id(:EscapedDbSchemaName)',
       ''
       );
+    qCastAsText: Result := 'CAST(%s AS NVARCHAR('+IntToStr(GRIDMAXDATA)+'))';
     else Result := inherited;
   end;
 end;

source/dbstructures.mysql.pas

@@ -3423,6 +3423,11 @@ function TMySqlProvider.GetSql(AId: TQueryId): string;
       'SELECT PLUGIN_NAME FROM INFORMATION_SCHEMA.PLUGINS WHERE PLUGIN_TYPE=''AUTHENTICATION'' AND PLUGIN_STATUS=''ACTIVE''',
       ''
       );
+    qCastAsText: Result := IfThen(
+      FServerVersion >= 40002,
+      'CAST(%s AS CHAR)',
+      ''
+      );
     else Result := inherited;
   end;
 end;

source/dbstructures.pas

@@ -52,7 +52,7 @@ interface
     qShowFunctionStatus, qShowProcedureStatus, qShowTriggers, qShowEvents, qShowCreateTrigger,
     qHelpKeyword, qShowWarnings, qGetEnumTypes,
     qDropUser, qCreateRole, qDropRole, qReloadPrivileges, qGrantRole, qRevokeRole, qSetDefaultRole,
-    qAutoInc, qIndexVisible, qIndexInvisible, qGetAuthPlugins);
+    qAutoInc, qIndexVisible, qIndexInvisible, qGetAuthPlugins, qCastAsText);
   TSqlProvider = class
     strict protected
       FNetType: TNetType;

source/dbstructures.postgresql.pas

@@ -743,6 +743,7 @@ function TPostgreSQLProvider.GetSql(AId: TQueryId): string;
       '' // ServerVersion < 9
       );
     qAutoInc: Result := 'SERIAL';
+    qCastAsText: Result := '%s::text';
     else Result := inherited;
   end;
 end;

source/dbstructures.sqlite.pas

@@ -427,6 +427,7 @@ function TSQLiteProvider.GetSql(AId: TQueryId): string;
     qGetCharsets: Result := 'SELECT ''UTF-8'' AS "Charset", ''UTF-8'' AS "Description" '+
       'UNION SELECT ''UTF-16le'', ''UTF-16 Little Endian'' '+
       'UNION SELECT ''UTF-16be'', ''UTF-16 Big Endian''';
+    qCastAsText: Result := 'CAST(%s AS CHAR)';
     else Result := inherited;
   end;
 end;