Join Query in Oracle Xpress Edition - inner-join

Question

Hello I am creating a table with name Category, inserted two rows.
When I am joining this table, output printed multiple rows.
My Table is:- Category
CREATE TABLE Category(
ID int NOT NULL Primary key,
Code varchar(50),
Name varchar(200),
Notes varchar(500),
Image1 varchar(250),
Image2 varchar(250),
Image3 varchar(250),
CreatedBy int NOT NULL,
PageTitle varchar(100),
MetaName varchar(200),
MetaDescription varchar(500),
MetaKeywords varchar(500),
ERPReferencesSysteID int,
ERPReferencesID int,
AssignedTo int,
Status int );
Insert Query:-
insert into Category values (902,'Code2', 'NAME2','Note2', 'Image12',
'Image22','Image32', 2016, 'PageTitle2','MetaName2', 'MetaDescription2',
'MetaKeyword2',02, 08, 2,1);
My Join Query:-
SELECT DISTINCT info.COLUMN_NAME AS NAME, info.OWNER AS TABLESCHEMA,
info.TABLE_NAME,UIC.COLUMN_POSITION AS POSITION,info.NULLABLE AS ISNULLABLE,
info.DATA_TYPE AS DATATYPE,tc.CONSTRAINT_TYPE AS CONSTRAINTTYPE,
tc.R_OWNER AS REFERENCESCHEMA FROM all_tab_columns
info join all_constraints tc on info.TABLE_NAME = tc.TABLE_NAME
join user_cons_columns rk on info.TABLE_NAME = rk.TABLE_NAME
join USER_IND_COLUMNS UIC on UIC.TABLE_NAME = info.TABLE_NAME
where info.TABLE_NAME= 'CATEGORY' AND info.owner ='SAN' ORDER BY
UIC.COLUMN_POSITION ASC;
When I am executing this join query rows are showing multiple times.
What i am doing wrong in this query?

Answer 1

Use INNER JOIN's for joining your tables.
SELECT DISTINCT info.COLUMN_NAME AS NAME, info.OWNER AS TABLESCHEMA,
info.TABLE_NAME,UIC.COLUMN_POSITION AS POSITION,info.NULLABLE AS ISNULLABLE,
info.DATA_TYPE AS DATATYPE,tc.CONSTRAINT_TYPE AS CONSTRAINTTYPE,
tc.R_OWNER AS REFERENCESCHEMA
FROM all_tab_columns info
INNER JOIN all_constraints tc ON info.TABLE_NAME = tc.TABLE_NAME
INNER JOIN user_cons_columns rk ON info.TABLE_NAME = rk.TABLE_NAME
INNER JOIN USER_IND_COLUMNS UIC ON UIC.TABLE_NAME = info.TABLE_NAME
WHERE info.TABLE_NAME = 'CATEGORY'
AND info.owner ='SAN'
ORDER BY UIC.COLUMN_POSITION ASC;

Answer 2

You have three constraints in the table; the primary key and two not-null constraints. One of those is redundant as the primary key column is implicitly not null anyway.
So there are three rows in user_cons_columns. Two of those are for id.
SELECT uc.constraint_name, uc.constraint_type, ucc.column_name
FROM user_constraints uc
JOIN user_cons_columns ucc ON ucc.constraint_name = uc.constraint_name
WHERE uc.table_name = 'CATEGORY';
CONSTRAINT_NAME C COLUMN_NAME
------------------------------ - --------------------
SYS_C00110620 C ID
SYS_C00110621 C CREATEDBY
SYS_C00110622 P ID
There is also one row in user_ind_columns for id, but not one for createdby, which is the other not-null constraint.
SELECT ui.index_name, uic.column_name
FROM user_indexes ui
JOIN user_ind_columns uic ON uic.index_name = ui.index_name
WHERE ui.table_name = 'CATEGORY';
INDEX_NAME COLUMN_NAME
------------------------------ --------------------
SYS_C00110622 ID
Both the id rows in user_cons_columns are matching with the one in user_ind_columns, so you get two rows in the result set. The distinct isn't helping because you are including the constraint type in the result set, so you see separate rows for P and C.
You are also not including the column_name in the joins; so all 16 row in all_tab_columns are joining to all three constraints and their columns. As you are using inner joins you seem to only want to show the primary key and its index, so this seems to be a long-winded way to do that:
SELECT distinct atc.column_name AS NAME, atc.owner AS tableschema,
atc.table_name, aic.column_position AS position, atc.nullable AS isnullable,
atc.data_type AS datatype, ac.constraint_type AS constrainttype,
ac.r_owner AS referenceschema
FROM all_tab_columns atc
JOIN all_constraints ac
ON ac.owner = atc.owner
AND ac.table_name = atc.table_name
JOIN all_cons_columns acc
ON acc.table_name = atc.table_name
AND acc.column_name = atc.column_name
JOIN all_ind_columns aic
ON aic.table_owner = atc.owner
AND aic.table_name = atc.table_name
AND aic.column_name = atc.column_name
WHERE atc.table_name= 'CATEGORY'
AND atc.owner = 'SAN'
AND ac.constraint_type = 'P'
ORDER BY aic.column_position ASC;
Which gets a single row for the P constraint ID column. If you intended to show all the columns you'd need outer joins.