Dynamic SQL with table name as a parameter

问题

I am trying to execute a procedure into which i send the table name and 2 column names as parameters:

EXECUTE IMMEDIATE 'select avg(@column1) from @Table1 where REF_D = @column2' into ATTR_AVG;

I have tried using the variables in combiations of '@', ':', '||' but nothing seems to work.

Has anyone used table names as a parameter. there are a few solutions here but for SQL Server

回答1:

You can only use bind variables (denoted by colons) for values, not for parts of the structure. You will have to concatenate the table and column names into the query:

EXECUTE IMMEDIATE 'select avg(' || column1 | ') from ' || Table1 
  || ' where REF_D = ' || column2 into ATTR_AVG;

Which implies REF_D is a fixed column name that can appear in any table you'll call this for; in a previous question that seems to be a variable. If it is actually a string variable then you'd need to bind and set that:

EXECUTE IMMEDIATE 'select avg(' || column1 | ') from ' || Table1 
  || ' where ' || column2 || ' = :REF_D' into ATTR_AVG using REF_D;

If it's supposed to be a date you should make sure the local variable is the right type, or explicitly convert it.

回答2:

You need to construct the executable statement using || (or else define it as one string containing placeholders that you can then manipulate with replace). Something like:

create or replace procedure demo
    ( p_table   user_tab_columns.table_name%type
    , p_column1 user_tab_columns.column_name%type
    , p_column2 user_tab_columns.column_name%type )
is
    attr_avg number;
begin
    execute immediate
        'select avg(' || p_column1 || ') from ' || p_table ||
        ' where ref_d = ' || p_column2
    into attr_avg;

    dbms_output.put_line('Result: ' || attr_avg);
end demo;

It's generally a good idea to build the string in a debugger-friendly variable first, i.e. something like:

create or replace procedure demo
    ( p_table   user_tab_columns.table_name%type
    , p_column1 user_tab_columns.column_name%type
    , p_column2 user_tab_columns.column_name%type )
is
    attr_avg number;
    sql_statement varchar2(100);
begin
    sql_statement :=
        'select avg(' || p_column1 || ') from ' || p_table ||
        ' where ref_d = ' || p_column2;

    execute immediate sql_statement into attr_avg;

    dbms_output.put_line('Result: ' || attr_avg);
end demo;

Depending on what ref_d is, you may have to be careful with what you compare it to, so the above could require some more work, but hopefully it gives you the idea.

Edit: however see Alex Poole's answer for a note about the use of bind variables. If ref_d is a variable that may need to become:

    sql_statement :=
        'select avg(' || p_column1 || ') from ' || p_table ||
        ' where ' || p_column2 || ' = :b1';

    execute immediate sql_statement into attr_avg using ref_d;

(The convention is to put the search expression on the right e.g. where name = 'SMITH' rather than where 'SMITH' = name, though they are the same thing to SQL.)

来源：https://stackoverflow.com/questions/43211749/dynamic-sql-with-table-name-as-a-parameter

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