I have a query using various joins, and I just need the list of columns which are returned by this query. I done it in java, by asking only one row with rownum=1 and getting column name for value.The problem is if there is no data returned by that query.
For ex.
select * from something
and if there is any data returning by this query then it will return col1,col2,col3.
But if there is no data returned by this query, then it will throw error.
What I need is
Is there any way that I can run
desc (select * from something)
or similar to get list of columns returned by query.
It can be in sql or JAVA. Both methods are acceptable.
In my application, user passes the query, and I can add wrapper to the query but I cant modify it totally.
The flow of application is
query from user -> execute by java and get one row -> return list of columns in the result set.
you can use ResultSetMetaData of resultset
for example :
ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM TABLE2");
ResultSetMetaData rsmd = rs.getMetaData();
int countOfColumns = rsmd.getColumnCount();
for(int i = 1; i <= countOfColumns ; i++ )
System.out.println(rsmd.getColumnName(i));
you could maybe convert your query to a view, you can then see the columns in the view by querying user_tab_columns
select * from user_tab_columns
The Oracle equivalent for information_schema.COLUMNS is USER_TAB_COLS for tables owned by the current user, ALL_TAB_COLS or DBA_TAB_COLS for tables owned by all users.
Tablespace is not equivalent to a schema, neither do you have to provide the tablespace name.
Providing the schema/username would be of use if you want to query ALL_TAB_COLS or DBA_TAB_COLS for columns OF tables owned by a specific user. in your case, I'd imagine the query would look something like:
String sqlStr= "
SELECT column_name
FROM all_tab_cols
WHERE table_name = 'users'
AND owner = ' || +_db+ || '
AND column_name NOT IN ( 'password', 'version', 'id' )
"
Note that with this approach, you risk SQL injection.
Related
I want to use procedure multiple times to get many table select from oracle database
My Oracle procedure
PROCEDURE getInfo(
Status IN VARCHAR2,
P_CUR OUT REFCURSOR)
AS
BEGIN
OPEN P_CUR FOR
SELECT *
FROM TABLE
WHERE TABLE.STATUS = Status
END;
Here is my Java call the the procedure. It doesn't work, I can not set registerOutParameter for PreparedStatement to get the cursor data.
PreparedStatement pstmt = null;
pstmt = cnn.prepareCall("{call " + schemaName + ".LOC_EXCHANGE.getInfo(?,?)}");
for (Entity entity : ListEntity) {
int i = 1;
pstmt.setString(i++, entity.getTxnId());
pstmt.registerOutParameter(i, OracleTypes.CURSOR);
pstmt.addBatch();
}
pstmt.executeBatch();
cnn.commit();
rs = (ResultSet) pstmt.getObject(i);
Fetching the data in bulk rather than in batch
I don't think you can batch those calls. You could probably do an anonymous block, instead:
BEGIN
LOC_EXCHANGE.getInfo(?, ?);
LOC_EXCHANGE.getInfo(?, ?);
LOC_EXCHANGE.getInfo(?, ?);
...
END;
Avoiding N+1
Personally, I think you're producing an N+1 problem here. rather than fetching data for each individual entity.getTxnId(), how about refactoring your getInfo() procedure to allow for returning data for a list of txnids? Do this:
CREATE TYPE txnids AS TABLE OF VARCHAR2(4000);
And then declare:
PROCEDURE getInfo(
Status IN txnids ,
P_CUR OUT REFCURSOR)
AS
BEGIN
OPEN P_CUR FOR
SELECT *
FROM TABLE
WHERE TABLE.STATUS IN (
SELECT * FROM TABLE (Status)
)
ORDER BY TABLE.STATUS
END;
Since you're projecting *, you'll still be able to access the STATUS column in order to group data in the client, after fetching it all.
I want to use jdbcTemplate to create table based on another table under condition. I have postgres database. When I execute this and pass parameter:
String SQL = "create table test as (select * from users where countryId =?)";
jdbcTemplate.update(SQL, new Object[] {3})
I receive table test with all columns from users table but with no rows.
However, when I execute this:
String SQL = "create table test as (select * from users where countryId =3)";
jdbcTemplate.update(SQL)
I receive test table with rows where countryId = 3, so that is what I was expecting to receive in the first solution.
Your passing of the bind variable is not correct, but it does not play any role.
You simple can not use a bind variable in a data definition statement as you immediately see in the triggered error
Caught: org.springframework.jdbc.UncategorizedSQLException:
PreparedStatementCallback; uncategorized SQLException for SQL
[create table test as (select * from users where countryId =?)];
SQL state [72000]; error code [1027];
ORA-01027: bind variables not allowed for data definition operations
So you have two options, either concatenate the statement (which is not recommended due to the danger of SQL injection)
or split the statement in two parts:
// create empty table
sql = "create table test as (select * from users where 1 = 0)";
jdbcTemplate.update(sql)
// insert data
sql = "insert into test(countryId, name) select countryId, name from users where countryId =?";
updCnt = jdbcTemplate.update(sql, new SqlParameterValue(Types.INTEGER,3));
Note that in the insert statement you can see the correct way of passing an interger value of 3 as a bind variable.
You can follow below approach as well:-
jdbcTemplate.execute("CREATE TABLE IF NOT EXISTS employee_tmp (id INT NOT NULL)");
List<Object[]> employeeIds = new ArrayList<>();
for (Integer id : ids) {
employeeIds.add(new Object[] { id });
}
jdbcTemplate.batchUpdate("INSERT INTO employee_tmp VALUES(?)", employeeIds);
Here you may query with 2 operations to avoid SQL injection.
You are using method update from jdbcTemplate in a wrong way.
Try with this:
String SQL = "create table test as (select * from users where countryId = ?)";
jdbcTemplate.update(SQL, 3);
I am trying to generate sql query based on user input. There are 4 search fields on the UI:
FIRST_NAME, LAST_NAME, SUBJECT, MARKS
Based on user input I am planning to generate SQL query. Input can be of any combination.
eg: select * from TABLE where FIRST_NAME="some_value";
This query needs to be generated when FIRST_NAME is given and other fields are null
select * from TABLE where FIRST_NAME="some_value" and LAST_NAME="some_value";
This query needs to be generated when FIRST_NAME and LAST_NAME are given and other fields are null
Since there are 4 input fields, number of possible queries that can be generated are 24 (factorial of 4).
One idea is to write if condition for all 24 cases.
Java pseudo code:
String QUERY = "select * from TABLE where ";
if (FIRST_NAME!=null) {
QUERY = QUERY + "FIRST_NAME='use_input_value';"
}
if (LAST_NAME!=null) {
QUERY = QUERY + "LAST_NAME='use_input_value';"
}
if (SUBJECT!=null) {
QUERY = QUERY + "SUBJECT='use_input_value';"
}
if (MARKS!=null) {
QUERY = QUERY + "MARKS='use_input_value';"
}
I am not able to figure out how to generate SQL queries with AND coditions for multiple Input values.
I have been through concepts on dynamically generate sql query but couldn't process further.
Can someone help me on this.
FYI: I have been through How to dynamically generate SQL query based on user's selections?, still not able to generate query string based on user input.
Let's think about what would happen if you just ran the code you wrote and both FIRST_NAME and LAST_NAME are provided. You'll wind up with this:
select * from TABLE where FIRST_NAME='use_input_value';LAST_NAME='use_input_value';
There are two problems here:
The query is syntactically incorrect.
It contains the literals 'use_input_value' instead of the values you want.
To fix the first problem, let's first add and to the start of each expression, and remove the semicolons, something like this:
String QUERY = "select * from TABLE where";
if (FIRST_NAME!=null) {
QUERY = QUERY + " and FIRST_NAME='use_input_value'";
}
Notice the space before the and. We can also remove the space after where.
Now the query with both FIRST_NAME and LAST_NAME will look like this:
select * from TABLE where and FIRST_NAME='use_input_value' and LAST_NAME='use_input_value'
Better but now there's an extra and. We can fix that by adding a dummy always-true condition at the start of the query:
String QUERY = "select * from TABLE where 1=1";
Then we append a semicolon after all the conditions have been evaluated, and we have a valid query:
select * from TABLE where 1=1 and FIRST_NAME='use_input_value' and LAST_NAME='use_input_value';
(It may not be necessary to append the semicolon. Most databases don't require semicolons at the end of a single query like this.)
On to the string literals. You should add a placeholder instead, and simultaneously add the value you want to use to a List.
String QUERY = "select * from TABLE where";
List<String> args = new ArrayList<>();
if (FIRST_NAME!=null) {
QUERY = QUERY + " and FIRST_NAME=?";
args.add(FIRST_NAME);
}
After you've handled all the conditions you'll have a string with N '?' placeholders and a List with N values. At that point just prepare a query from the SQL string and add the placeholders.
PreparedStatement statement = conn.prepareStatement(QUERY);
for (int i = 0; i < args.size(); i++) {
statement.setString(i + 1, args[i]);
}
For some reason columns and parameters are indexed starting at 1 in the JDBC API, so we have to add 1 to i to produce the parameter index.
Then execute the PreparedStatement.
Greeting to all smart people around here !!
I have faced a weird interview question regarding SQL.
Qn . If I have 100 tables in Database. I want to fetch common records from Each table.
For example, location is common field in 100 tables. I want to fetch location field from all the tables without mentioning each table name in my SQL query.
Is there any way to do it?
If any possibilities let me know...
get list of tables from db metadata, and then query with each:
Statement stmt = conn.createStatement();
ResultSet locationRs = null;
DatabaseMetaData md = conn.getMetaData();
ResultSet rs = md.getTables(null, null, "%", null);
while (rs.next()) {
locationRs = stmt.executeQuery("SELECT location from "+ rs.getString(3));
System.out.println(locationRs.getString(1));
}
In MSSQL Server you have INFORMATION_SCHEMA.COLUMNS table that contains the column names so you can use group by and having count some value you will get the column name after that you can use pivot to get the values of column names and carry on to it. You will get the ans.
For eg.
Select COLUMN_NAME from INFORMATION_SCHEMA.COLUMNS group BY COLUMN_NAME having count(COLUMN_NAME) > 2
By above query you will get the common column names
You can try this for any Number of Tables in a DB :
select COLUMN_NAME from INFORMATION_SCHEMA.COLUMNS group by COLUMN_NAME having count(COLUMN_NAME)=(select count(*) from INFORMATION_SCHEMA.TABLES)
My friend has found answer for my question..
To get common column from multiple tables,Use INFORMATION_SCHEMA.COLUMNS and common column name.
Query :
select *from information_schema.columns where column_name='column name'
Hope this will helpful !
I am assuming you already have connection and statemnt object's. Now try the below; it might work for you, if not make some adjustments with loops and conditions. Also, you need to have two ResultSet Objects ex: rs1 and rs2. DatabaseMetaData dbmd = con.getMetaData();
String table[] = {"TABLE"} `;
rs1 = dbmd.getTable(null, null, ".*" ,table);
while(rs1.next()){
String tableFrom = rs1.getString(3) ;
rs2 = dbmd.getColumns(null,null,tableFrom , ".*") ;
while(rs2.next()) {
String locColFrom = rs2.getString(3);
if(locColFrom .equalsIgnoreCase("location"))
stmt.executeQuery(select locColFrom from tableFrom ) ;
}
}
Here's an link to study [Oracle] (http://docs.oracle.com/javase/7/docs/api/java/sql/DatabaseMetaData.html#getTables(java.lang.String,%20java.lang.String,%20java.lang.String,%20java.lang.String[]))
i have two tables "Table1" with columns user_name,Password and course ID and another table "course" with columns course_id,course_name.I have used the following code to display the course ID from Table1 according to the user_name received from the login page.using ResultSet rs1.now i want to retrieve the course_name from the table "course" according to the course ID receieve from "Table1".for that in the second query pstmt2.setString(1, ); what parameter i should use to get the course_id value from the previous query
HttpSession sess=request.getSession();
String a=(String)sess.getAttribute("user");
String b=(String)sess.getAttribute("pass");
try {
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Connection con=DriverManager.getConnection("jdbc:odbc:ggg");
Statement st = con.createStatement();
String query="select * from Table1 where user_name=?";
PreparedStatement pstmt=con.prepareStatement(query);
pstmt.setString(1,a);
ResultSet rs1=pstmt.executeQuery();
while(rs1.next())
out.println("<h3>COURSE ID: "+rs1.getString("course ID")+"<h3>");
String query2="SELECT * from course where course_id=?";
PreparedStatement pstmt2=con.prepareStatement(query2);
pstmt2.setString(1,);
ResultSet rs2=pstmt2.executeQuery();
while(rs2.next())
{
out.println("<h3>course name: "+rs2.getString("course_name")+"<h3>");
}
why do you go for two turns of database hit, even though you created one time connection object.
modify the query as below
SELECT * from course where course_id = (select course_id from Table1 where user_name=?);
from this query you noneed to give input of courseid also.
No need to hit database twice to get the results that you need. use the query
Select table1.course_id, course.course_name from table1, course where table1.course_id=course_id and table1.user_name=?
This should set the course_id parameter:
pstmt2.setString(1,rs1.getString("course_id"));
Or, as I see the "course_id" column may have a different name in "Table1":
pstmt2.setString(1,rs1.getString("course ID"));
As the other post mentioned there's no need to go to another set of query. Try this example query:
SELECT course.course_id, course.course_name
FROM table1 t1
INNER JOIN course c
ON t1.course_id = c.course_id
WHERE t1.user_name = ?;
Now if you insist your coding the parameter o your pstmt2.setString(1,); is:
pstmt2.setString(1,rs1.getString("course_id")); //or course ID defending on your column name