Database advanced learning notes -- SQL statement

sql The classification of
1. static state sql：select * from emp where empno=7788;
-- static state sql Referring to PL/SQL Block sqL Statements are explicit at compile time , It's about identifying objects
2. dynamic sql:select * from emp where empno=' Parameters ';
-- dynamic sql It means in PL/SQL Block compile time sql The statement is indeterminate , For example, different operations are performed according to the parameters entered by the user
( The parameter could be sql sentence , Numbers , written words )

------ dynamic sql-----
dynamic sql： Is to put sql Written in a string , Parse the string in the stored procedure to execute sql.
--（1） Execution dynamics sql Several ways to
（1）& Parameter input
（2） Use open-for,fetch and close sentence （ The cursor ）
For processing dynamic multi row query operations , have access to oPEN-FOR Statement open cursor ,
Use FETCH Statement loop extract data , End use CLOSE Statement close cursor .
（3） Use batch dynamic statements
That is, in the dynamic sql Use in BULK Clause , Or when using cursor variables fetch Use in BULK, Or in the FORALL Use in statement
(4) Use what the system provides PL/soL package DBMs_sQL To achieve dynamic sQL
(5) Use EXECUTE IMMEDIATE sentence
Include DDL sentence ,DCL sentence ,DNL Statements and single line sELECT sentence . This method cannot be used to process multi line query statements
-- dynamic sql The role of
（1） Can support DDl sentence , static state sql Can only support DML sentence
（2） Support WEB The inquiry intention of the quoting program
（3） You can put the business logic in the table first , Then dynamically compile
-- Use EXECUTE IMMEDIATE Statement execution is dynamic sql-----------
static state sql Embed yourself in plsql In the sentence , And dynamic sql Statements produce different sql sentence .
grammar ：
execute immediate Dynamic statement string
[into Variable list ]
[using parameter list ]
explain ：
Dynamic statement string ： Store the specified sql Statements or plsql String variable of block
into： Used to store query results
using： Parameters pass values
dynamic sql Format of parameters ：[: Parameter name ], Parameters need to be used at run time using Pass value

-- Usage dynamics sql Operation to create a table -------------
— Sort PL/sQL In programming , stay DML And transaction control statements can be used directly sql,
however DDL Statement and system control statement can't be in PL/sql You can use ,
To achieve in pL/sql Use in DDL Statements and system control statements , You can use dynamic sql To achieve
-- The wrong way to write
begin
create tables test1000 as select * from emp;
end;
-- Correct writing 1( Neither pass parameters nor assign values )
begin
execute immediate 'create table test1000 as select * from emp ';
end;
select * from test1000;
-- Correct writing 2( Store the result set in variables and run dynamically )
declare
sqls varchar2(100);
begin
sqls:='create table test1001 as select * from emp ';
execute immediate sqls;
end;
select * from test1001;

-------- dynamic sql Transfer parameter and assignment -----------
using The ginseng
into assignment
Parameter format [: Parameters ]
--- Query salary according to employee number
--- Write three ： Transfer parameter and assignment
declare 
v_sal emp.sal%type;
begin
   -- Execution dynamics sql
  execute immediate 'select sal from emp where empno=: Parameters '
  -- Variable assignment
      into v_sal
  -- Receiving parameters
  using & Enter employee number ;
  dbms_output.put_line(' Wages '||v_sal);
  end;
--------- dynamic sql Statement does not pass parameters , Assign only --------------
--- example ： Query salary according to employee number
----- Write four ： Don't pass it on , Assign only
declare
v_sal emp.sal%type;
begin
 execute immediate 'select sal from emp where empno=7788'
 into v_sal;
 dbms_output.put_line(v_sal);
end;

------ Example ----------
-- Create a stored procedure , By passing the table name , Delete the corresponding table ( Method 2)??????
create or replace procedure truncate_table(table_name in varchar2)
is
sqls varchar2(100);
begin
sqls:='truncate table'||table_name;
execute immediate sqls;
end;

begin
truncate_table('test1001');
end;
select * from test1001;
-- Syntax for creating tables ----------------------------
create table Table name （
Field name Field type ）
-- Create table ： Create a table according to the table name, field name and other parameters entered by the user
create or replace procedure create_table(
table_name in varchar2,---- Table name
field1 in varchar2,--- Field 1
field1type in varchar2,--- Field 1 Data type of
field2 in varchar2,--- Field 2
field2type in varchar2,--- Field 2 Data type of
field3 in varchar2,--- Field 3
field3type in varchar2--- Field 3 Data type of The last parameter is not followed by a comma
)
is 
sqls varchar2(500);
begin
  sqls:='create table'||' '||table_name||'('||field1||' '||field1type||','||field2||' '
  ||field2type||','||field3||' '||field3type||')';
  execute immediate sqls;
end;
-- Call the stored procedure to create the table ??????--- Insufficient authority (sys user )
begin
create_table('test_table','id','varchar2(100)','name','varchar2(100)','age','varchar2(100)');
end;

-- insert data （sys user ）---------------------------------------
create or replace procedure insert_table(
id in varchar2,
name in varchar2,
age  in varchar2
)
is
sqls varchar2(500);
begin
  sqls:='insert into test_table values(:1,:2,:3)';
  execute immediate sqls using id,name,age;
end;
-- call

begin
insert_table('1',' Xiaohong ','18');
end;

select * from test_table;