我不断获取记录中的重复数据

Question

I am using MS access.

I tried write SQL code that refer to the tables EMPLOYEE, PROJECT and JOB and return the results as shown in the figure below:

PROJ_NAME PROJ_VALUE PROJ_BALANCE EMP-LNAME EMP_FNAME EMP_INITIAL JOB_CODE JOB_DESCRIPTION    JOB_CHG_HOUR
iCEBUTT   800.00     12000        SMITH     ANNE      E           12       ELECTRIC ENGENEER  10
FIREBUTT  810.00     20000        SHEMAN    ANNE      G           15       WATER ENGENEER     12
iCEBTEA   802.00     10000        SIMPSON   ANNE      H           11       NON ENGENEER       11
iCECUBE   890.00     18000        SMITFIELD ANNE      A           19       ELECTRIC ENGENEER  9.5

MY CODE

SELECT  PROJ_NAME, PROJ_VALUE, PROJ_BALANCE, EMP_LNAME, EMP_FNAME, EMP_INITIAL,            JOB_CODE, JOB_DESCRIPTION, JOB_CHG_HOUR
FROM EMPLOYEE, JOB, PROJECT
WHERE PROJ_VALUE >= 10000;

what I got from my code is a lot of duplicate datas. My result:

PROJ_NAME PROJ_VALUE PROJ_BALANCE EMP-LNAME EMP_FNAME EMP_INITIAL JOB_CODE JOB_DESCRIPTION    JOB_CHG_HOUR
iCEBUTT   800.00     12000        SMITH     ANNE      E           12       ELECTRIC ENGENEER  10
iCEBUTT   800.00     12000        SMITH     ANNE      E           12       ELECTRIC ENGENEER  10
iCEBUTT   800.00     12000        SMITH     ANNE      E           12       ELECTRIC ENGENEER  10
iCEBUTT   800.00     12000        SMITH     ANNE      E           12       ELECTRIC ENGENEER  10
FIREBUTT  810.00     20000        SHEMAN    ANNE      G           15       WATER ENGENEER     12
FIREBUTT  810.00     20000        SHEMAN    ANNE      G           15       WATER ENGENEER     12
FIREBUTT  810.00     20000        SHEMAN    ANNE      G           15       WATER ENGENEER     12
FIREBUTT  810.00     20000        SHEMAN    ANNE      G           15       WATER ENGENEER     12
iCEBTEA   802.00     10000        SIMPSON   ANNE      H           11       NON ENGENEER       11
iCEBTEA   802.00     10000        SIMPSON   ANNE      H           11       NON ENGENEER       11
iCEBTEA   802.00     10000        SIMPSON   ANNE      H           11       NON ENGENEER       11
iCECUBE   890.00     18000        SMITFIELD ANNE      A           19       ELECTRIC ENGENEER  9.5
iCECUBE   890.00     18000        SMITFIELD ANNE      A           19       ELECTRIC ENGENEER  9.5
iCECUBE   890.00     18000        SMITFIELD ANNE      A           19       ELECTRIC ENGENEER  9.5

Answer 1

You are missing the condition for the joins. Now both employee and job give all records. You have to tell how they relate to the project table.

Something like this:

SELECT  p.PROJ_NAME, p.PROJ_VALUE, p.PROJ_BALANCE, p.EMP_LNAME, p.EMP_FNAME, p.EMP_INITIAL,            p.JOB_CODE, p.JOB_DESCRIPTION, p.JOB_CHG_HOUR
FROM EMPLOYEE e, JOB j, PROJECT p
WHERE p.job_code = j.job_code /*enter correct fields here*/
AND   p.emp_name = e.emp_name /*enter correct fields here*/
AND   p.PROJ_VALUE >= 805000.00;

The field names I used are based on your current query. I hope there are some ID fields you could use instead.

Preferably use real join s:

SELECT  p.PROJ_NAME, p.PROJ_VALUE, p.PROJ_BALANCE, p.EMP_LNAME, p.EMP_FNAME, p.EMP_INITIAL,            p.JOB_CODE, p.JOB_DESCRIPTION, p.JOB_CHG_HOUR
FROM PROJECT p
JOIN JOB j
ON   p.job_code = j.job_code /*enter correct fields here*/
JOIN EMPLOYEE e
ON   p.emp_name = e.emp_name /*enter correct fields here*/
WHERE p.PROJ_VALUE >= 805000.00;

Answer 2

You have created a Cartesian product (or cross join). The valus obtained are not only duplicates but also wrong. To avoid this, you need to use joins in your query.

SELECT *
FROM EMPLOYEE 
JOIN JOB ON EMPLOYEE.JOB_ID = JOB.ID
JOIN PROJECT ON EMPLOYEE.PROJ_ID = PROJECT.ID
WHERE PROJECT.PROJ_VALUE >= 805000.00;

Check this tutorial for some insight on using SQL joins.

Answer 3

Without seeing the actual duplicate data you are receiving or the structure of the tables, it is hard to answer... but I assume that it is because you aren't limiting the joins of the tables...

Such as

SELECT *
FROM EMPLOYEE e
JOIN Job j on j.JobID = e.JobID
JOIN Project p on p.ProjectID  = e.ProjectID (or j.ProjectID?)

You need to limit the data the secondary tables are returning... as you have it now, the secondary tables will return all.

Outer or inner join used depending on how you have them tied together...

Answer 4

You are using a join on three tables: Employee, Job and Project, but add no join conditions. This creates duplicates. Consider adding conditions like this:

SELECT  PROJ_NAME, PROJ_VALUE, PROJ_BALANCE, EMP_LNAME, EMP_FNAME, EMP_INITIAL,                JOB_CODE, JOB_DESCRIPTION, JOB_CHG_HOUR
FROM EMPLOYEE, JOB, PROJECT
WHERE PROJ_VALUE >= 805000.00
AND JOB.EMPLOYEE_ID=EMPLOYEE.ID
AND PROJECT.JOB_ID = JOB.ID;