Combine tables in select based on criteria in a column SQLServer - sql-server

Question

I have two tables (each with about 20 columns), none of the column names match up but some of the values in 1 column match the values in another (see below).
I want to get a the combination of the 2 tables on certain columns based on True/False values in a column on the primary table.
I am doing all of this using the SQLServer Third Party JDBC Drivers in Oracle's SQL Developer (I am not sure if or how that might have an effect on my syntax).
I am sure that this is simple, but I cannot find any examples that do this and I am just too new to SQL to wrap my head around it.
CREATE TABLE [dbo].[TableA] (
[colA1] VARCHAR (10) NULL,
[colA2] VARCHAR (10) NULL,
[colA3] VARCHAR (10) NULL,
[colA4] VARCHAR (10) NULL,
[colA5] VARCHAR (10) NULL,
[colA6] INT NULL,
[colKey] INT NOT NULL,
CONSTRAINT [PK_TableA] PRIMARY KEY CLUSTERED ([colKey] ASC)
);
CREATE TABLE [dbo].[TableB] (
[colB1] VARCHAR (10) NULL,
[colB2] VARCHAR (10) NULL,
[colB3] VARCHAR (10) NULL,
[colB4] INT NULL,
[colKey] INT NOT NULL,
PRIMARY KEY CLUSTERED ([colKey] ASC)
);
INSERT INTO TableA(colKey,colA1,colA2,colA3,colA4,colA5,colA6) VALUES (1,'AC1-1','AC2-1','AC3-1',NULL,'FALSE',2016);
INSERT INTO TableA(colKey,colA1,colA2,colA3,colA4,colA5,colA6) VALUES (2,'AC1-2','AC2-2','AC3-2',NULL,'FALSE',2016);
INSERT INTO TableA(colKey,colA1,colA2,colA3,colA4,colA5,colA6) VALUES (3,'AC1-3',NULL,NULL,'AC4-3','TRUE',2016);
INSERT INTO TableA(colKey,colA1,colA2,colA3,colA4,colA5,colA6) VALUES (4,'AC1-4',NULL,NULL,'AC4-4','TRUE',2016);
INSERT INTO TableA(colKey,colA1,colA2,colA3,colA4,colA5,colA6) VALUES (5,'AC1-5','AC2-5','AC3-5',NULL,'FALSE',2015);
INSERT INTO TableA(colKey,colA1,colA2,colA3,colA4,colA5,colA6) VALUES (6,'AC1-6','AC2-6','AC3-6',NULL,'FALSE',2015);
INSERT INTO TableA(colKey,colA1,colA2,colA3,colA4,colA5,colA6) VALUES (7,'AC1-7',NULL,NULL,'AC4-7','TRUE',2015);
INSERT INTO TableA(colKey,colA1,colA2,colA3,colA4,colA5,colA6) VALUES (8,'AC1-8',NULL,NULL,'AC4-8','TRUE',2015);
INSERT INTO TableA(colKey,colA1,colA2,colA3,colA4,colA5,colA6) VALUES (9,'AC1-9',NULL,NULL,'AC4-9','TRUE',2016);
INSERT INTO TableB(colKey,colB1,colB2,colB3,colB4) VALUES (1,'AC4-3','BC2-1','BC3-1',2015);
INSERT INTO TableB(colKey,colB1,colB2,colB3,colB4) VALUES (2,'AC4-4','BC2-2','BC3-2',2015);
INSERT INTO TableB(colKey,colB1,colB2,colB3,colB4) VALUES (3,'AC4-4','BC2-3','BC3-3',2016);
INSERT INTO TableB(colKey,colB1,colB2,colB3,colB4) VALUES (4,'AC4-3','BC2-4','BC3-4',2016);
INSERT INTO TableB(colKey,colB1,colB2,colB3,colB4) VALUES (5,'AC4-7','BC2-5','BC3-5',2015);
INSERT INTO TableB(colKey,colB1,colB2,colB3,colB4) VALUES (6,'AC4-8','BC2-6','BC3-6',2015);
TableA
+-------+--------+--------+--------+-------+-------+
| colA1 | colA2 | colA3 | colA4 | colA5 | colA6 |
+-------+--------+--------+--------+-------+-------+
| AC1-1 | AC2-1 | AC3-1 | (Null) | FALSE | 2016 |
| AC1-2 | AC2-2 | AC3-2 | (Null) | FALSE | 2016 |
| AC1-3 | (Null) | (Null) | AC4-3 | TRUE | 2016 |
| AC1-4 | (Null) | (Null) | AC4-4 | TRUE | 2016 |
| AC1-5 | AC2-5 | AC3-5 | (Null) | FALSE | 2015 |
| AC1-6 | AC2-6 | AC3-6 | (Null) | FALSE | 2015 |
| AC1-7 | (Null) | (Null) | AC4-7 | TRUE | 2015 |
| AC1-8 | (Null) | (Null) | AC4-8 | TRUE | 2015 |
| AC1-9 | (Null) | (Null) | AC4-9 | TRUE | 2016 |
+-------+--------+--------+--------+-------+-------+
TableB
+-------+-------+-------+-------+
| colB1 | colB2 | colB3 | colB4 |
+-------+-------+-------+-------+
| AC4-3 | BC2-1 | BC3-1 | 2015 |
| AC4-4 | BC2-2 | BC3-2 | 2015 |
| AC4-4 | BC2-3 | BC3-3 | 2016 |
| AC4-3 | BC2-4 | BC3-4 | 2016 |
+-------+-------+-------+-------+
Results Table
+-------+--------+-------+-------------------------+-------------------------+
| colA1 | colA4 | colA5 | combined(colA2 & colB2) | combined(colA3 & colB3) |
+-------+--------+-------+-------------------------+-------------------------+
| AC1-1 | (null) | FALSE | AC2-1 | AC3-1 |
| AC1-2 | (null) | FALSE | AC2-2 | AC3-2 |
| AC1-3 | AC4-3 | TRUE | BC2-1 | BC3-1 |
| AC1-4 | AC4-4 | TRUE | BC2-2 | BC3-2 |
| AC1-9 | AC4-9 | TRUE | (null) | (null) |
+-------+--------+-------+-------------------------+-------------------------+
So I think I need some kind of SELECT like this:
SELECT colA1, colA5,
IF colA5 = True
THEN colB2, colB3, etc.
ELSE colA2, ColA3, etc.
FROM tableB, tableA
WHERE colA1 = colB1 AND colB4 = 2016 AND colA6 = 2016
I have tried this:
SELECT A.colA1
,A.colA4
,A.colA5
,CASE
WHEN A.colA5 = TRUE
THEN B.colB2
ELSE A.colA2
END AS 'combined(colA2 & colB2)'
,CASE
WHEN A.colA5 = TRUE
THEN B.colB3
ELSE A.colA4
END AS 'combined(colA3 & colB3)'
,
FROM TableA A
,TableB B
WHERE A.colA6 = '2016'
AND B.colB4 = '2016'
AND (
A.colA4 = B.colB1
OR A.colA4 IS NULL
)
what I get is this:
+-------+-------+-------+-------------------------+-------------------------+
| colA1 | colA4 | colA5 | combined(colA2 & colB2) | combined(colA3 & colB3) |
+-------+-------+-------+-------------------------+-------------------------+
| AC1-3 | AC4-3 | TRUE | BC2-1 | BC3-1 |
| AC1-4 | AC4-4 | TRUE | BC2-2 | BC3-2 |
+-------+-------+-------+-------------------------+-------------------------+
So I am missing the rows were TableA/colA5 are FALSE. Also, I need 12 of these "combined" columns, is there a way that I can avoid using 12 CASE statements?

Answer 1

After learning about joins and case here is the answer (though apparently I will have to use the 12 CASE statements that I would have preferred to avoid).
SELECT A.colA1
,A.colA4
,A.colA5
,CASE
WHEN A.colA5 = 'TRUE'
THEN B.colB2
ELSE A.colA2
END AS 'combined(colA2 & colB2)'
,CASE
WHEN A.colA5 = 'TRUE'
THEN B.colB3
ELSE A.colA3
END AS 'combined(colA3 & colB3)'
FROM TableA A LEFT JOIN TableB B ON A.colA4 = B.colB1
WHERE (A.colA6 = '2016' and A.colA5 ='FALSE')
or (A.colA6 = '2016' and A.colA5 ='true' and B.colB4 = '2016')
or (A.colA6 = '2016' and A.colA5 ='true' and B.colB4 is null)
;