当前位置：网站首页>Anchor type and row data type of DB2 SQL pl

Anchor type and row data type of DB2 SQL pl

2022-06-10 18:45:00 【Blue black 2020】

Environmental Science

operating system ：Ubuntu 20.04
Db2：11.5.0.0

Anchor data type

An anchor type is a type defined based on another database object , Like columns 、 Global variables 、SQL Variable etc. .

The difference between an anchor variable and a normal variable is , The former will be quoted to something specific . Look at it this way , I feel that the anchor type is somewhat similar to “ Foreign keys ” The concept of .

Create table tab1 and tab2 as follows ：

CREATE TABLE tab1(col1 INT, col2 CHAR)

INSERT INTO tab1 VALUES (1,2)

INSERT INTO tab1 VALUES (3,4)

CREATE TABLE tab2 (col1a INT, col2a CHAR)

create a file test1.sql as follows ：

CREATE OR REPLACE PROCEDURE p1()
BEGIN
  DECLARE var1 ANCHOR tab1.col1;

  SELECT col1 INTO var1 FROM tab1 WHERE col2 = 2;

  INSERT INTO tab2 VALUES (var1, 'a');
END@

CALL p1()@

Run script test1.sql , as follows ：

*  temp0527 db2 -[email protected] -f test1.sql
DB20000I  The SQL command completed successfully.

  Return Status = 0

See the table tab2 , It can be seen that there is an additional line of records ：

*  temp0527 db2 "select * from tab2"

COL1A       COL2A
----------- -----
          1 a    

  1 record(s) selected.

In this case , Anchor variable var1 Defined as reference tab1 Tabular col1 Column , Next, assign a value to the... Of a specific row col1 The value of the column , Finally, it can be used as a general variable var1 .

Be careful , to var1 assignment , There can be no value that satisfies the condition , But there cannot be more than one value that satisfies the condition .

If SELECT col1 FROM tab1 WHERE col2 = 2 The result is empty. , be var1 The value of is NULL , No problem （ This is also consistent with foreign keys , The value of the foreign key can be null , That is, no specific values are referenced ）;
If SELECT col1 FROM tab1 WHERE col2 = 2 The result has multiple values , May be an error ;

establish test2.sql The documents are as follows ：

CREATE OR REPLACE PROCEDURE p2(in var1 anchor tab1.col1)
BEGIN
  INSERT INTO tab2 VALUES (var1, 'b');
END@

CALL p2(100)@

function test2.sql Script , as follows ：

*  temp0527 db2 -[email protected] -f test2.sql
DB20000I  The SQL command completed successfully.

  Return Status = 0

The result was a bit unexpected , 100 Not at all tab1 Tabular col1 Value of field , But there's no mistake , tab2 A line was inserted in the (100, 'b') The record of . In this case , That statement is anchor tab1.col1 What's the use ？

Row data type

Line variable , seeing the name of a thing one thinks of its function , It represents a line of records .

To use row variables , You need to create row data types first , such as ：

create or replace type myrow as row(c1 int, c2 varchar(100))

Then you can declare the line variables , such as ：

declare r1 myrow

When creating row variables , Each of these fields is initialized to NULL value .

The following types of values can be assigned to row variables ：

literal

set r1 = (1, 'aaa')

expression

values (1, 'aaa') into r1

Function return value

set r1 = f1()

Other variables

set r1 = r2

Be careful ： r1 and r2 Must be of the same or compatible type . If r1 and r2 Is a completely different data type myrow1 and myrow2 , Even if myrow1 and myrow2 Same definition , It can't pass set r1 = r2 To assign a value , Because the two types are incompatible .

Query results

set r1 = (select c1, c2 from t1)

Be careful ： Must be 0 Row or single row results .

NULL

Be careful ： Each field is set to NULL , But the row variable itself is not NULL .

Row variable assignment method ：

set

See the previous example .

values into

See the previous example .

select into

select 1, 'aaa' into r1 from sysibm.sysdummy1

fetch into

declare c1 cursor for select 1, 'aaa' from sysibm.sysdummy1;

open c1;

fetch c1 into r1;

close c1;

For fields of row variables （ namely < Line variable >.< Column > ） The type and manner of assignment is similar to that of assignment to row variables .

You cannot directly compare two row variables , Only its field values can be compared .

Can be in insert Statement using line variables , such as ：

insert into t1 values r1

Equivalent to ：

insert into t1 values (r1.c1, r1.c2)

Can be in a insert Insert multiple row variables into the statement ：

insert into t1 values r1, r2

Let's look at a complete example .

create a file test3.sql as follows ：

create or replace type myrow as row(c1 int, c2 varchar(100))@

set serveroutput on@

begin
	declare r1, r2 myrow;

	declare c1 cursor for select 3, 'ccc' from sysibm.sysdummy1;

	set r1 = (1, 'aaa');

	call dbms_output.put_line('1)' || r1.c1 || ', ' || r1.c2);

	set r2 = r1;

	call dbms_output.put_line('2)' || r2.c1 || ', ' || r2.c2);

	set r1 = null;

	call dbms_output.put_line('3)' || coalesce(cast(r1.c1 as varchar(100)), '') || ', ' || coalesce(r1.c2, ''));

	select 2, 'bbb' into r1 from sysibm.sysdummy1;

	call dbms_output.put_line('4)' || r1.c1 || ', ' || r1.c2);

	open c1;

	fetch c1 into r1;

	close c1;

	call dbms_output.put_line('5)' || r1.c1 || ', ' || r1.c2);
end@

set serveroutput off@

drop type [email protected]

Run script test3.sql , as follows ：

* temp0527 db2 -[email protected] -f test3.sql 
DB20000I  The SQL command completed successfully.

DB20000I  The SET SERVEROUTPUT command completed successfully.

DB20000I  The SQL command completed successfully.

1)1, aaa
2)1, aaa
3), 
4)2, bbb
5)3, ccc

DB20000I  The SET SERVEROUTPUT command completed successfully.

DB20000I  The SQL command completed successfully.

notes ： stay 3) It's about , because NULL After splicing with other strings, it is still NULL , So here we use coalesce() Function will NULL To '' , however int Type of NULL and '' Are not compatible , So first cast to varchar type , And then use coalesce() function .