Throw better error when trying to modify schema while using unsupported dialect (#3609)

lib/schema/compiler.js

@@ -14,6 +14,12 @@ function SchemaCompiler(client, builder) {
   this.sequence = [];
 }
 
+function throwOnlyPGError(operationName) {
+  throw new Error(
+    `${operationName} is not supported for this dialect (only PostgreSQL supports it currently).`
+  );
+}
+
 Object.assign(SchemaCompiler.prototype, {
   pushQuery: pushQuery,
 
@@ -25,6 +31,19 @@ Object.assign(SchemaCompiler.prototype, {
 
   createTableIfNotExists: buildTable('createIfNot'),
 
+  createSchema: () => {
+    throwOnlyPGError('createSchema');
+  },
+  createSchemaIfNotExists: () => {
+    throwOnlyPGError('createSchemaIfNotExists');
+  },
+  dropSchema: () => {
+    throwOnlyPGError('dropSchema');
+  },
+  dropSchemaIfExists: () => {
+    throwOnlyPGError('dropSchemaIfExists');
+  },
+
   alterTable: buildTable('alter'),
 
   dropTablePrefix: 'drop table ',