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It s Your Turn to Declare Parameters
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You ll have plenty of practice declaring parameters in the coming chapters. So I want you to do this instead: 1. Go get a snack. 2. Eat it. 3. Take a quick nap. 4. Start on 4.
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At this point, you should be a master of variable and parameter declarations. And you should understand the scope in which they are accessible. You should also be wary of any lunchtime conversation with someone who wants to sell you a NULL. There s nothing in it for you. Next, let s start working with some SQL in our PL/SQL.
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Whoa! One Statement at a Time, Please!
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ow we begin our journey of using SQL in PL/SQL. We ll start out slowly, inserting one row at a time, then updating one row at a time, then deleting one row at a time, and finally selecting one row at a time. I take this approach because you first have to insert data into a database before you can update, delete or select it. I call these kinds of SQL statements singletons, because they return one set of results. So let s get started by putting some data into the database.
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No, I m not talking about those annoying cards you find in books or magazines when you first open them. The context here is inserting data into a relational database. To insert data into a relational database from PL/SQL, you simply write a SQL INSERT statement, where the values are PL/SQL literals, PL/SQL variables, or SQL columns. I m going to start with the worst of all examples, and then continually improve its architecture and design as we progress through the chapter. To start out, you ll see what most PL/SQL programmers do, and then how to improve the code. Please keep in mind that there is a time and place for each of these solutions. In the end, you re the one who will need to make the decision about which is the best solution based on the business problem you re solving. Rarely do you just perform a simple atomic INSERT statement in PL/SQL. You can do that using a SQL*Plus script, without using PL/SQL at all. More often, you ll want to insert or update depending on whether the data you intend to insert already exists in the database. If it does, you ll probably want to check to see if you need to update the values already in the database. So the process you decide to use to insert and/or update becomes a proverbial chicken vs. egg dilemma which do you do first Let s start by looking at what can happen if a duplicate row already exists. You re going to have to put up with seeing me use SELECT when I INSERT, because, in a modern database design, you need to SELECT sequence and code ID values to use them in an INSERT statement. Let s check it out. Listing 4-1 is an anonymous PL/SQL procedure that inserts values into the WORKER_T table.
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CHAPTER 4 WHOA ! ONE STATEMEN T A T A TIM E, PLEA SE!
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Listing 4-1. An Insert Example Using PL/SQL Literals and Variables, insert.sql 001 002 003 004 005 006 007 008 009 010 011 012 013 014 015 016 017 018 019 020 021 022 023 024 025 026 027 028 029 030 031 032 033 034 035 036 037 038 039 040 041 042 043 044 045 rem rem rem rem insert.sql Donald J. Bales on 12/15/2006 An anonymous PL/SQL procedure to insert values using PL/SQL literals and variables
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set serveroutput on size 1000000; declare -- I declared these variables so I can get -- the required ID values before I insert. n_id WORKER_T.id%TYPE; n_worker_type_id WORKER_T.worker_type_id%TYPE; v_external_id WORKER_T.external_id%TYPE; n_gender_id WORKER_T.gender_id%TYPE; -- I'll use this variable to hold the result -- of the SQL insert statement. n_count number; begin -- First, let's get the worker_type_id for a contractor begin select worker_type_id into n_worker_type_id from WORKER_TYPE_T where code = 'C'; exception when OTHERS then raise_application_error(-20002, SQLERRM|| ' on select WORKER_TYPE_T'|| ' in filename insert.sql'); end; -- Next, let's get the gender_id for a male begin select gender_id into n_gender_id from GENDER_T where code = 'M'; exception when OTHERS then raise_application_error(-20004, SQLERRM|| ' on select GENDER_T'||
CHAPTER 4 WHOA ! ONE STATEMEN T A T A TIM E, PLEA SE!
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' in filename insert.sql'); end; -- Now, let's get the next id sequence begin select WORKER_ID_SEQ.nextval into n_id from SYS.DUAL; exception when OTHERS then raise_application_error(-20001, SQLERRM|| ' on select WORKER_ID_SEQ.nextval'|| ' in filename insert.sql'); end; -- And then, let's get the next external_id sequence begin select lpad(to_char(EXTERNAL_ID_SEQ.nextval), 9, '0') into v_external_id from SYS.DUAL; exception when OTHERS then raise_application_error(-20003, SQLERRM|| ' on select EXTERNAL_ID_SEQ.nextval'|| ' in filename insert.sql'); end; -- Now that we have all the necessary ID values -- we can finally insert a row! begin insert into WORKER_T ( id, worker_type_id, external_id, first_name, middle_name, last_name, name, birth_date, gender_id ) values ( n_id, -- a variable n_worker_type_id, -- a variable v_external_id, -- a variable 'JOHN', -- a literal 'J.', -- a literal 'DOE', -- a literal
CHAPTER 4 WHOA ! ONE STATEMEN T A T A TIM E, PLEA SE!
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'DOE, JOHN J.', -- a literal to_date('19800101', 'YYYYMMDD'), -- a function n_gender_id ); -- a variable n_count := sql%rowcount; exception when OTHERS then raise_application_error(-20005, SQLERRM|| ' on insert WORKER_T'|| ' in filename insert.sql'); end; pl(to_char(n_count)||' row(s) inserted.'); end; / commit; The SQL INSERT syntax used in Listing 4-1 is as follows:
INSERT INTO <table_name> ( <column_name_1>, <column_name_2>,... <column_name_N> ) VALUES ( <column_value_1>, <column_value_2>,... <column_value_N> ); where <table_name> is the name of the table to INSERT VALUES INTO, <column_name> is the name of a column in the table, and <column_value> is the value for a corresponding <column_name>. The column values can be PL/SQL literals, variables, qualifying function results, or SQL column values. You should always use a list of columns in your INSERT statements in order to maintain the validity of your code, in case someone later adds a column to a table definition (and, in practice, that happens). Let s break down the code in Listing 4-1: Lines 12 through 15 declare four variables to hold the ID values from related sequence and code tables. Line 19 declares a number to hold the resulting row count from the INSERT statement. Lines 25 through 28 contain a SELECT statement to get the worker_type_id value for a contractor. On lines 24 through 34, I ve blocked (put the code in a nested PL/SQL block) the SELECT statement so I can catch any catastrophic error, and report it to the presentation layer with an error number and message that are unique to the PL/SQL program. This practice greatly simplifies troubleshooting. You ll know exactly what went wrong and where it went wrong, and that s nice.
CHAPTER 4 WHOA ! ONE STATEMEN T A T A TIM E, PLEA SE!
On lines 37 through 47, I get the gender_id value for a male. On lines 50 through 59, I get the next id sequence value, storing that value in variable n_id. On lines 62 through 71, I get the next external_id value. I use the SQL function to_char() to do an explicit data type conversion from numeric to character. I wrap the character value with the SQL function lpad() in order to left-pad the number string with zeros so it s nine characters long. Lines 76 through 95 contain an INSERT statement to insert John Doe s data into the WORKER_T table. Lines 77 through 85 list the names of the columns I m going to insert values INTO. This is an important practice. If I didn t list the columns, the procedure would become invalid any time someone modified the WORKER_T table. Lines 87 through 95 specify the column values using a combination of PL/SQL literals, PL/SQL variables, and even the return value of the SQL function to_date() for the value of column birth_date. On line 97, I store the result value of the INSERT statement, which is the number of rows inserted. To accomplish this, I use the pseudo-cursor name sql% and its variable rowcount. On lines 75 through 103 collectively, I ve blocked the INSERT statement so I can detect and report the exact type and location of an error in the PL/SQL procedure. The following is the output from the first time the insert.sql script is executed: SQL> @insert.sql 1 row(s) inserted. PL/SQL procedure successfully completed. If you examine the code in Listing 4-1 and its output, you ll see that the procedure inserted one row into the database, as reported by the output from the INSERT statement through the sql%rowcount variable. But what happens if we run the script again Here s the output from the script s second execution: SQL> @insert.sql declare * ERROR at line 1: ORA-20005: ORA-00001: unique constraint (BPS.WORKER_T_UK2) violated on insert WORKER_T in filename insert.sql ORA-06512: at line 93
CHAPTER 4 WHOA ! ONE STATEMEN T A T A TIM E, PLEA SE!
No PL/SQL procedure successfully completed message this time! An unhandled unique constraint exception was raised as an application error, number 20005, along with a meaningful message. Now if you want to handle this particular kind of exception, you can use one of three tactics: Catch exception DUP_VAL_ON_INDEX (good) Use additional PL/SQL code to predetect the duplicate s presence (better) Use additional SQL code to predetect the duplicate s presence (best) Let s take a look at these solutions, from good to best.
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