Through practical examples, this post explained how to count the unique values from a table. Use the DISTINCT clause with the aid of the SELECT statement to get and describe the unique table records. To count only unique rows, you must specify a DISTINCT clause with the COUNT() function. The simple COUNT() function retrieves all the rows/records, including duplicate values and null. In PostgreSQL, the DISTINCT clause can be used with the COUNT() function to count only unique/distinct values of a table. However, the DISTINCT clause skipped the duplicate names and retrieved only unique values. In the actual result set, JOHN occurs two times while JOE occurs three times. This way, you can count the number of unique records however, you can fetch the unique rows from the desired table using the DISTINCT clause as follows: SELECT DISTINCT emp_name The COUNT() function returned '5' this time, proving that it only counts unique values. Run the below command to count only unique values from the emp_record table: SELECT COUNT(DISTINCT emp_name) Output retrieves ‘8’, which proves that the COUNT() function counted each record, including duplicates. Now use the COUNT() function to count the number of rows in the emp_record table: SELECT COUNT(emp_name) There are eight records in the emp_record table. Let’s run the below command to see the table’s data: SELECT * FROM emp_record We will insert multiple records into the emp_record table including some duplicates: INSERT INTO emp_record(emp_name, emp_age, emp_salary) Use the DISTINCT Clause with the COUNT() function to count only the unique values: COUNT(DISTINCT col_name) Įxample: How to Count Distinct Values in Postgres?įirstly, we will create a sample table named emp_reocrd with four columns: emp_id, emp_name, emp_age, and emp_salary. How to Count Distinct/Unique Values in Postgres? This write-up is going to present a detailed guide on how to count unique values through practical examples. However, the DISTINCT clause can be used with the COUNT() function to count only unique/distinct values of a table. It retrieves the number of all records/rows, including duplicate/redundant records and null values. If not good enought split stock name to own table.PostgreSQL provides a built-in function named COUNT() that counts the number of records in a table. Tldr try pk index on time and one index on stock, or try time+stock composite index. But that having better relational table structure then allows you to have pk on time and/or stock (assuming that your usage is where clause has usually time filter ) This way you get all distinct stock names fast from stock table, getting distinct stock per time needs join. Of course on insert you need to figure first unique_id for stock, that can be done with with insert on conflict clause. and fill stock table with unique id's and stock names. that will help whole usage.Īnother solution is create stock table that has bigint identity and stock name, change intraday stock to stock_id. If index on stock or stock and time wont be enough (i assume that you compare stock values by time or you aggregate hourly/daily values per stock. Naming convention forces you to escape all column names "Stock", recommended way is not to use "Stock" but just name stock. "intraday_pkey" PRIMARY KEY, btree ("Stock", "Time") SELECT, COUNT() OVER() as total - here FROM ( SELECT DISTINCT ON (serialno) id, serialno, name, timestamp FROM productinfo INNER JOIN my.account ON id accountid WHERE lower(name) 'hello' ORDER BY serialno. Volume | double precision | | | | plain | | | Also, you can not include DISTINCT keyword within window functions - it has not been implemented yet (as of Postgres 9.6). Low | double precision | | | | plain | | |Ĭlose | double precision | | | | plain | | | High | double precision | | | | plain | | | Open | double precision | | | | plain | | | Time | timestamp with time zone | | not null | | plain | | | Stock | text | | not null | | extended | | | Table structure as text: Table "public.intraday"Ĭolumn | Type | Collation | Nullable | Default | Storage | Compression | Stats target | Description With my previous setup, I could simply just check the number of tables.Īny recommendations on how to go about this? But if I simply use COUNT(DISTINCT "Stock") it will take hours since I have billions of rows. The first hurdle I run into is this: I'd like to check if I have both daily and intraday data for all the stocks in my ticker list - to check that the data download and load into Postgres has worked. Now I've switched to a 2 tables total structure. I had previously set up a database of stock market data with a 2 tables per ticker structure (1min and daily aggregation periods).
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