# 1. Motivation
PL-SQL (Stored procedure) is a collection of sql, which is defined and used similarly to functions. It supports conditional judgments, loops and other control statements, supports cursor processing of result sets, and can write business logic in SQL.
Hive uses Hplsql to support PL-SQL and is largely compatible with Oracle, Impala, MySQL, Redshift, PostgreSQL, DB2, etc. We support PL-SQL in Doris based on Hplsql to achieve compatibility with Stored procedures of database systems such as Oracle and PostgreSQL.
Reference documentation:
Hive: http://mail.hplsql.org
Oracle: https://docs.oracle.com/en/database/oracle/oracle-database/21/lnpls/plsql-language-fundamentals.html#GUID-640DB3AA-15AF-4825-BD6C-1D4EB5AB7715
Mysql: https://dev.mysql.com/doc/refman/8.0/en/create-procedure.html
# 2. Implementation
Take the following case as an example to explain the process of connecting Doris FE to execute stored procedures using the Mysql protocol.
```
CREATE OR REPLACE PROCEDURE A(IN name STRING, OUT result int)
select count(*) from test;
select count(*) into result from test where k = name;
END
declare result INT default = 0;
call A(‘xxx’, result);
print result;
```
1. Add procedure and persist the Procedure Name and Source (raw SQL) into Doris FE metadata.
2. Call procedure, extract the actual parameter Value and Procedure Name in Call Stmt. Use Procedure Name to find the Source in the metadata, extract the Name and Type of the Procedure parameter, and match them with the actual parameter Value to form a complete variable <Name, Type, Value>.
3. Execute Doris Statement
- Use Doris Logical Plan Builder to parse the Doris Statement syntax in Source, replace parameter variables, remove the into variable clause, and generate a Plan Tree that conforms to Doris syntax.
- Use stmtExecutor to execute SQL and encapsulate the query result set iterator into QueryResult.
- Output the query results to Mysql Channel, or write them into Cursor, parameters, and variables.
- Stored Programs compatible with Mysql protocol support multiple statements.
4. Execute PL-SQL Statement
- Use Plsql Logical Plan Builder to parse and execute PL-SQL Statement syntax in Source, including Loop, Cursor, IF, Declare, etc., and basically reuse HplSQL.
# 3. TODO
1. Support drop procedure.
2. Create procedure only in `PlSqlOperation`.
3. Doris Parser supports declare variable.
4. Select Statement supports insert into variable.
5. Parameters and fields have the same name.
6. If Cursor exits halfway, will there be a memory leak?
7. Use getOriginSql(ctx) in syntax parsing LogicalPlanBuilder to obtain the original SQL. Is there any problem with special characters?
8. Supports complex types such as Map and Struct.
9. Test syntax such as Package.
10. Support UDF
11. In Oracle, create procedure must have AS or IS after RIGHT_PAREN,
but Mysql and Hive not support AS or IS. Compatibility issues with Oracle will be discussed and resolved later.
12. Built-in functions require a separate management.
13. Doris statement add stmt: egin_transaction_stmt, end_transaction_stmt, commit_stmt, rollback_stmt.
14. Add plsql stmt: cmp_stmt, copy_from_local_stmt, copy_stmt, create_local_temp_table_stmt, merge_stmt.
# 4. Some questions
1. JDBC does not support the execution of stored procedures that return results. You can only Into the execution results into a variable or write them into a table, because when multiple result sets are returned, JDBC needs to use the prepareCall statement to execute, otherwise the Statemnt of the returned result executes Finalize. Send EOF Packet will report an error;
2. Use PL-SQL Cursor to open multiple Query result set iterators at the same time. Doris BE will cache the intermediate status of these Queries (such as HashTable) and query results until the Query result set iteration is completed. If the Cursor is not available for a long time Being used will result in a lot of memory waste.
3. In plsql/Var.defineType(), the corresponding Plsql Var type will be found through the Mysql type name string, and the corresponding relationship between Doris type and Plsql Var needs to be implemented.
4. Currently, PL-SQL Statement will be forwarded to Master FE for creation and calculation, which may affect other services on Doris FE and is limited by the performance of Doris FE. Consider moving it to Doris BE for execution.
5. The format of the result returned by Doris Statement is ```xxxx\n, xxxx\n, 2 rows affected (0.03 sec)```. PL-SQL uses Print to print variable values in an unformatted format, and JDBC cannot easily obtain them. Real results.
# 5. Some thoughts
The above execution of Doris Statement reuses Doris Logical Plan Builder for syntax parsing, parses it from top to bottom into a Plan Tree, and calls stmtExecutor for execution. PL-SQL replacement variables, removal of Into Variable and other operations are coupled in Doris syntax parsing. The advantage is that it is easier to It can be compatible with Doris grammar with a few changes, but the disadvantage is that it will invade the Doris grammar parsing process.
HplSQL performs a syntax parsing independently of Hive to implement variable substitution and other operations, and finally outputs a SQL that conforms to Hive syntax. The following is a simple syntax parsing process for select, where, expression, table name, join, The parsing of agg, order and other grammars must be re-implemented. The advantage is that it is completely independent from the original system, but the changes are too complicated.
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