Oracle sql updating multiple tables english man dating
drop table t; drop table s; create table t (id number, name varchar2(32)); create table s (id number, name varchar2(32)); insert into t values (1,'1'); insert into t values (2,'2'); insert into t values (3,'3'); insert into t values (4,'4'); insert into t values (5,'5'); insert into s values (3,'three'); insert into s values (5,'five'); select * from t; update t set name = (select name from s where = s.id); select * from t; Our first table (t) simply has the numbers 1-5 in the 'id' and 'name' column but we want to update some of the names based on the contents of the second table (s) but this table only has values for two of the rows. 1 rows inserted 1 rows inserted 1 rows inserted 1 rows inserted 1 rows inserted 1 rows inserted 1 rows inserted ID NAME ---------------------- -------------------------------- 1 1 2 2 3 3 4 4 5 5 5 rows selected 5 rows updated ID NAME ---------------------- -------------------------------- 1 2 3 three 4 5 five 5 rows selected The problem here is that the update isn't a true 'join' as every row is going to be updated and if the 'join' fails then a null is written.This is OK so long as we can preserve the 'default' numeric values. If we consider what we’ve learned so far – Select, Update, Insert, Delete – as unicellular organisms, what we’re about to Part 1, Part 2, Part 3 A wise man* once said: To build the Great Wall of China, you must start with a brick. There are two types of outer joins; a left outer join allows nulls in the second table in our join, while a right outer join allows nulls in the first table (while showing all records from the table on the right).In our previous articles we acquainted ourselves with our bricks; now it’s time to build. The syntax is as follows: Run the query and notice how the resultset now contains all your friends, including those who do not have a phone number.You’ve probably already guessed that I’m setting you up, but it’s important that we make these mistakes now, so we can learn about them. But what if Rachel had told us that she was changing her phone number next month and we’d put in a future end-date? The above query will give you many, many rows that look identical; however, if you replace the column list with an asterisk (*) and rerun the query, you’ll notice that the records aren’t exactly identical, each has one column different. PHONE_ID; in our select list) exist in two or more of our tables, we must always tell Oracle which one we are referring to every time we use that column name. Excluding all end-dated rows now would give us the wrong result. But we don’t want to hard-code the date into our query, in case we want to rerun the query next week.
Question: I want to update multiple rows in my table, and I need to understand how to update multiple columns.
If we consider what we’ve learned so far – Select, Update, Insert, Delete – as unicellular organisms, what we’re about to do next is multicellular, big and beautiful – it’s like going from an amoeba to a bee, a butterfly, to Beyoncé. Notice how, by using a left outer join, we got all the rows in friend_name (the table on the left of the join); change it to a right outer join and see how that changes the output. But we need to add a third table – PHONE_NUMBER – to our query to make it useful. Joining multiple tables in this way is a little like baking a cake; you apply your joins layer by layer.
[*that wise man was me] Consider a real-world requirement that we might have of our Addressbook database; since it contains a list of our friends and their phone numbers, we will naturally want to see a list of their names and their phone numbers. Our friends’ names are in the FRIEND_NAME table, while their phone numbers are in the PHONE_NUMBER table. My data and yours might now be very different because of all the practising you’ve been doing (you have been practising, haven’t you? PHONE_NUMBER FROM FRIEND_NAME FN, FRIEND_PHONE FP, PHONE_NUMBER PN WHERE FN. (NB: I’ve never baked a cake before, but I once saw someone bake a cake on TV, and I remember thinking, “Hey, that’s just like writing an outer join query!
You may have already figured out why; it only returns friends that have a phone number.
START_DATE, SYSDATE) Our query is a thing of beauty, but you must have noticed that it does not return a complete list of our friends.