diff --git a/pages/总复习2023t1.md b/pages/总复习2023t1.md
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 							- Physical database design
 					- LATER SQL
 						- purpose and importance of SQL.
+							- SQL is a transform-oriented language with 2
+							  major components: #flashcard
+								- A DDL for defining database structure.
+									- Create table
+									- Drop table
+								- A DML for retrieving and updating data.
+									- Insert
+									- Delete
+									- update
+									- Select
 						- retrieve data from database and formulate queries using SELECT and
 							- Use compound WHERE conditions.
 							- Sort query results using ORDER BY.