use
SELECT count( DISTINCT(email) ) FROM orders
Distinct provide unique email ids and then simply count them.
More Related Contents:
- Error related to only_full_group_by when executing a query in MySql
- Find duplicate records in MySQL
- How to declare a variable in MySQL?
- Can you split/explode a field in a MySQL query?
- MySQL order by before group by
- MySQL Cannot Add Foreign Key Constraint
- Which is fastest? SELECT SQL_CALC_FOUND_ROWS FROM `table`, or SELECT COUNT(*)
- Grouping into interval of 5 minutes within a time range
- ERROR 1044 (42000): Access denied for user ”@’localhost’ to database ‘db’
- Difference between float and decimal data type
- Convert timestamp to date in MySQL query
- Update a column value, replacing part of a string
- Parse date in MySQL
- mysql dynamic query in stored procedure
- mysql: get record count between two date-time
- Difference between these two joining table approaches?
- MySQL INT meaning
- Get total number of rows when using LIMIT? [duplicate]
- Table is specified twice, both as a target for ‘UPDATE’ and as a separate source for data in mysql
- MySQL export into outfile : CSV escaping chars
- Simple Random Samples from a MySQL Sql database
- MySQL LAST_INSERT_ID() used with multiple records INSERT statement
- MySQL Select minimum/maximum among two (or more) given values
- MySQL: Many tables or many databases?
- Select only last value using group by at mysql
- MySQL errorno 121
- How can I “select *” from a table in MySQL but omit certain columns?
- For homebrew mysql installs, where’s my.cnf?
- Force MySQL to return duplicates from WHERE IN clause without using JOIN/UNION?
- comparison of truncate vs delete in mysql/sqlserver [duplicate]