Embedded SQL in PostgreSQL

Transcription

1 March 24, 2011

2 Michael Meskes Since 1993 Free Software Since 1994 Linux Since 1995 Debian GNU/Linux Since 1998 PostgreSQL

3 Michael Meskes Ph.D Project Manager Branch Manager since 2000 President

4 Embedded SQL Embedded SQL is a method of combining the computing power of a programming language and the database manipulation capabilities of SQL. take from wikipedia

5 PostgreSQL Programming result = PQexec(conn, "SELECT * FROM foo;"); num_rows = PQntuples(result); field = PQfnumber(result "attribute"); value = PQgetvalue(result, current_row, field); isnull = PQgetisnull(result, current_row, field); size = PQgetlength(result, current_row, field); type = PQftype(result, field);

6 Concepts of Embedded SQL SQL-Standard Ordinary C program with embedded SQL Preprocessor (ECPG) transforms SQL-Code into library calls SQL-Syntax is checked during preprocessor run Better accessability of data between C and SQL

7 Example #include <stdlib.h> #include <stdio.h> int main(int argc, char *argv[]) { puts("hello"); EXEC SQL UPDATE tabelle SET a = a + 1; }

8 Example /* Processed by ecpg (4.6.0) */ /* These include files are added by the preprocessor */ #include <ecpglib.h> #include <ecpgerrno.h> #include <sqlca.h> /* End of automatic include section */ #line 1 "a.pgc" #include <stdlib.h> #include <stdio.h> int main(int argc, char *argv[]) { puts("hello"); { ECPGdo( LINE, 0, 1, NULL, 0, ECPGst_normal, "update tabelle set a = a + 1", ECPGt_EOIT, ECPGt_EORT);} #line 9 "a.pgc" }

9 Connecting EXEC SQL CONNECT TO dbname AS connname USER user; For example: EXEC SQL CONNECT TO tcp:postgresql://sql.beispiel.de:5432/mydb AS myconn USER peter IDENTIFIED BY secret ;

10 Close connection EXEC SQL DISCONNECT; -- close current connection EXEC SQL DISCONNECT connname;

11 Execute SQL commands EXEC SQL CREATE TABLE foo (number integer, ascii char(16)); EXEC SQL INSERT INTO foo (number, ascii ) VALUES (9999, doodad ); EXEC SQL DELETE FROM foo WHERE number = 9999; EXEC SQL UPDATE foo SET ascii = foobar WHERE number = 9999 ;

12 Autocommit The default configuration doesn t do COMMIT automatically. So don t forget to do it yourself: EXEC SQL COMMIT;

13 Commands with host variables (1) EXEC SQL BEGIN DECLARE SECTION; int v1; char v2[100]; EXEC SQL END DECLARE SECTION; v1 = 42; strcpy(v2, "text"); EXEC SQL INSERT INTO test VALUES (:v1, :v2); EXEC SQL COMMIT;

14 Commands with host variables (2) EXEC SQL BEGIN DECLARE SECTION; int v1; VARCHAR v2[40]; EXEC SQL END DECLARE SECTION; EXEC SQL DECLARE foo CURSOR FOR SELECT a, b FROM test; do { EXEC SQL FETCH NEXT FROM foo INTO :v1, :v2; } while ();

15 Translated #line 2 "a.pgc" int v1, ind1 ; #line 3 "a.pgc" struct varchar_v2_1 { int len; char arr[ 40 ]; } v2 ; /* exec sql end declare section */ #line 4 "a.pgc" /* declare foo cursor for select a, b from test */ #line 6 "a.pgc" { ECPGdo( LINE, 0, 1, NULL, 0, ECPGst_normal, "declare foo cursor for select a, b from test", } #line 7 "a.pgc" do { { ECPGdo( LINE, 0, 1, NULL, 0, ECPGst_normal, "fetch next from foo", ECPGt_EOIT, ECPGt_int,&(v1),(long)1,(long)1,sizeof(int), ECPGt_NO_INDICATOR, NULL, 0L, 0L, 0L, ECPGt_varchar,&(v2),(long)40,(long)1,sizeof(struct varchar_v2_1), ECPGt_NO_INDICATOR, NULL, 0L, 0L, 0L, ECPGt_EORT);} #line 11 "a.pgc" } while ();

16 Null Values EXEC SQL INSERT INTO test(id, val) VALUES(2, :intvar :nullind); EXEC SQL SELECT val INTO :intvar :nullind from test; EXEC SQL UPDATE test SET val = :intvar :nullind;

17 Error Trapping: Callbacks EXEC SQL WHENEVER SQLERROR STOP; EXEC SQL WHENEVER SQLWARNING SQLPRINT; EXEC SQL WHENEVER SQLERROR CALL func();

18 Error Trapping: SQLCA struct { char sqlcaid[8]; long sqlabc; long sqlcode; struct { int sqlerrml; char sqlerrmc[70]; } sqlerrm; char sqlerrp[8]; long sqlerrd[6]; char sqlwarn[8]; char sqlstate[5]; } sqlca;

19 Compile sources with ecpg ecpg prog1.pgc # (erzeugt prog1.c) cc -c -I/usr/include/postgresql prog1.c # (erzeugt prog1.o) cc -o prog prog1.o -lecpg # (erzeugt prog) Makefiles make things easier...

20 Informix Compatibility $int j = 3; $CONNECT TO :dbname; $CREATE TABLE test(i INT PRIMARY KEY, j INT); $INSERT INTO test(i, j) VALUES (7, :j); $COMMIT; $CLOSE; Additional types Additional embedded SQL statements Informix-compatible SQLDA Descriptor Areas Additional functions Additional constants

21 Migrationen EXEC SQL CONNECT SQL-Migration Variables Changes to the precompiler possible Compatibility layer

22 History Linus Tolke Import to Postgres early 1998 Compatibility layer 2003

23 Current Versions Precompiler Library 6.2 Types Library 3.1 Compatibility Library 3.2

24 Further Development On-going Performance, e.g. Auto-Prepare Standardfeatures, e.g. SQLDA Compatibility

25 We need YOU! Remarks? Feedback? Requests?