使用链接表的SQL插入/删除行查询

Question

I have 4 sql tables that have linked rows based on a common city. Each table row has a code that will be combined together to create 1 master code based on the code value of each table row with a matching city. For example, if Table_1.code = 2, Table_2.code = 3c, Table_3.code = 1a, and Table_4.code = 2(2) matching the city of Houston then the combined end result code value would be 2-3c-1a-2(2). I have a query that uses inner joins that works fine to create the combined code based on the matching city. My problem is, sometimes I will not have a child table 2(Chapter), 3(Part) or 4(Section) code row for a city since it might come later. How's the best way to do an insert where I can add a table 2(Chapter), 3(Part) or 4(Section) code row that matches the city of the parent table_1 row and will update all FK references on other tables so that the table rows are linked together by city for a another query to get the combined code later if needed. I'm not an expert at SQL programming, but was wondering if someone could guide me in how this could be done. Hopefully, I've setup the tables correctly so that each row will have a FK reference to a prev/next table in the list that matches the city code, so rows can be inserted or deleted anywhere in between the table_1(title) parent to table_4(section) for a particular city. Can someone help me w/ an insert and delete query to handle this condition above using the following tables below.

Table1-Title (Parent table)
 table1_ID_PK int,
 code varchar(100),
 city varchar(100)

Table2-Chapter (Child table)
 table2_ID_PK int,
 table1_ID_FK int,
 table3_ID_FK int,
 code varchar(100),
 city varchar(100)

Table3-Part (Child table)
 table3_ID_PK int,
 table1_ID_FK int,
 table2_ID_FK int,
 table4_ID_FK int,
 code varchar(100),
 city varchar(100)

Table4-Section (Child table)
 table4_ID_PK int,
 table1_ID_FK int,
 table2_ID_FK int,
 table3_ID_FK int,
 code varchar(100),
 city varchar(100)

Answer 1

what I can suggest is to use VIEW, so whenever all parts are available in the view, you can then insert them wherever you want. The view will always updated automatically. So, you can use your current query, and adjust it to use it in the view, and then query that view, if it has the full code you need, then you can insert that row to the target table.

Example :

CREATE VIEW CityMasterCode AS (
    SELECT 
        t1.City 
    ,   CASE WHEN t1.code IS NULL OR t1.code = '' THEN NULL ELSE t1.code +  '-' END 
    +   CASE WHEN t2.code IS NULL OR t2.code = '' THEN NULL ELSE t2.code +  '-' END 
    +   CASE WHEN t3.code IS NULL OR t3.code = '' THEN NULL ELSE t3.code +  '-' END 
    +   CASE WHEN t4.code IS NULL OR t4.code = '' THEN NULL ELSE t4.code END AS MasterCode
    FROM 
        table1 t1
    LEFT JOIN table2 t2 ON t2.table1_ID_FK = t1.table1_ID_PK
    LEFT JOIN table3 t3 ON t3.table1_ID_FK = t1.table1_ID_PK
    LEFT JOIN table4 t4 ON t4.table1_ID_FK = t1.table1_ID_PK
)


INSERT INTO TargetTable (city, code)
SELECT 
    m.City 
,   m.MasterCode
FROM table1 t1 
JOIN CityMasterCode m ON m.City = t1.City AND t1.code = m.MasterCode

UPDATE answering your question in the comments. If you want to use UPDATE CASCADE, you need to set FK action to UPDATE CASCADE. This mean, whenever the PK updated, all its FK will be updated as well. So, in your case, you'll need to make the Code for each table as PK, this will also means your code column will be always unique. This approach for your scenario will be not a good idea.

However, since I've got the idea you're trying to do (kinda), I would suggest to change the way of your thinking. Instead of going this road, you can use just one table that will contain Title, Chapter, Part, and Section codes. and update them as needed. which will be much easier for you.

it would be something like this :

MasterCityCode (Child Table)
ID_PK int,
table1_ID_FK int,
city varchar(100), 
TitleCode varchar(100),
ChapterCode varchar(100),
PartCode varchar(100),
SectionCode varchar(100)

And the parent table will be holding the city and master code, which will be updated whenever all 4 parts in MasterCityCode table are completed (Triggers are useful for this part).

Quick Example:

First creating the required tables :

CREATE TABLE CityCode (
    ID INT IDENTITY(1,1) NOT NULL,
    City VARCHAR(100) NOT NULL, 
    Code VARCHAR(100) NULL,
    PRIMARY KEY (ID, City)  
)

CREATE TABLE CityCode_Master (
    ID INT IDENTITY(1,1) NOT NULL,
    CityCode_ID_FK INT NOT NULL,
    CityCode_City_FK  VARCHAR(100) NOT NULL, 
    TitleCode VARCHAR(100) NULL,
    ChapterCode VARCHAR(100) NULL,
    PartCode VARCHAR(100) NULL,
    SectionCode VARCHAR(100) NULL, 
    PRIMARY KEY (ID),
    FOREIGN KEY (CityCode_ID_FK, CityCode_City_FK) REFERENCES CityCode(ID, City)
    ON UPDATE CASCADE 
    ON DELETE CASCADE
)   

Now, we will set two triggers one on CityCode, which will insert all new cities in CityCode_Master table. The other one will be on CityCode_Master, which will handle the CityCode.code update. So, if all code parts are not null then it'll update the CityCode.code with the new master code.

CREATE TRIGGER InsertNewRowInCityCode_Master
   ON  CityCode
   AFTER INSERT
AS 
BEGIN
    SET NOCOUNT ON;

    INSERT INTO CityCode_Master (CityCode_ID_FK, CityCode_City_FK)  
    SELECT ID, City
    FROM 
        inserted
END

GO
CREATE TRIGGER UpdateCityCode
   ON  CityCode_Master
   FOR UPDATE
AS 
BEGIN
    SET NOCOUNT ON;

    IF EXISTS (
        SELECT * 
        FROM inserted 
        WHERE 
            TitleCode IS NOT NULL 
        AND ChapterCode IS NOT NULL 
        AND PartCode IS NOT NULL 
        AND SectionCode IS NOT NULL     
    )
    BEGIN 

        UPDATE city
        SET Code = TitleCode + '-' + ChapterCode + '-' + PartCode + '-' +  SectionCode
        FROM CityCode city 
        JOIN inserted ins ON ins.CityCode_ID_FK = city.ID AND ins.CityCode_City_FK = city.City 
    END 

END

now, let's try them out.

we will insert a new city in CityCode table.

INSERT INTO CityCode (City)
VALUES ('Houston')

if you query CityCode table, you'll find that code for Houston is NULL, which is what we need for the first stage, and if you query CityCode_Master table, you'll find a new row for Houston, and all other code columns are null.

Now, let's update the CityCode_Master codes.

for a single code :

-- Update a single column at time. 
UPDATE CityCode_Master
SET TitleCode = '2'
WHERE 
    CityCode_ID_FK = 1 
AND CityCode_City_FK = 'Houston'

if you recheck the table, you'll find that only column TitleCode is updated, the rest of the codes still null, and if you recheck CityCode table, you'll still see that code for Houston is still null.

Now let's update the rest of them to see the affects of the second trigger :

UPDATE CityCode_Master
SET 
    ChapterCode = '3c'
,   PartCode    = '1a'
,   SectionCode = '2(2)'
WHERE 
    CityCode_ID_FK = 1 
AND CityCode_City_FK = 'Houston'

you'll see that in CityCode_Master all the codes are not null now. If you go back to CityCode table and recheck it, you'll find that code column for Houston is now updated with the master code 2-3c-1a-2(2)

I hope this will help you