How can I find non-ASCII characters in MySQL

Question

I m working with a MySQL database that has some data imported from Excel  The data contains non-ASCII characters  em dashes  etc   as well as hidden carriage returns or line feeds  Is there a way to find these records using MySQL

User · Accepted Answer

It depends exactly what you re defining as  ASCII   but I would suggest trying a variant of a query like this   SELECT   FROM tableName WHERE columnToCheck NOT REGEXP   A-Za-z0-9      That query will return all rows where columnToCheck contains any non-alphanumeric characters  If you have other characters that are acceptable  add them to the character class in the regular expression  For example  if periods  commas  and hyphens are OK  change the query to   SELECT   FROM tableName WHERE columnToCheck NOT REGEXP   A-Za-z0-9  -      The most relevant page of the MySQL documentation is probably 12 5 2 Regular Expressions

User · Answer

You can define ASCII as all characters that have a decimal value of 0 - 127  0x00 - 0x7F  and find columns with non-ASCII characters using the following query  SELECT   FROM TABLE WHERE NOT HEX COLUMN  REGEXP     0-7  0-9A-F         This was the most comprehensive query I could come up with

User · Answer

One missing character from everyone s examples above is the termination character   0    This is invisible to the MySQL console output and is not discoverable by any of the queries heretofore mentioned  The query to find it is simply   select   from TABLE where COLUMN like    0

User · Answer

In Oracle we can use below   SELECT   FROM TABLE A WHERE ASCIISTR COLUMN A   lt  gt  COLUMN A

User · Answer

This is probably what you re looking for   select   from TABLE where COLUMN regexp     -       It should return all rows where COLUMN contains non-ASCII characters  or non-printable ASCII characters such as newline

User · Answer

Try Using this query for searching special character records  SELECT   FROM tableName WHERE fieldName REGEXP    a-zA-Z0-9       -    amp

User · Answer

Try Using this query for searching special character records  SELECT   FROM tableName WHERE fieldName REGEXP    a-zA-Z0-9       -    amp

User · Answer

In Oracle we can use below   SELECT   FROM TABLE A WHERE ASCIISTR COLUMN A   lt  gt  COLUMN A

User · Answer

MySQL provides comprehensive character set management that can help with this kind of problem   SELECT whatever   FROM tableName   WHERE columnToCheck  lt  gt  CONVERT columnToCheck USING ASCII    The CONVERT col USING charset  function turns the unconvertable characters into replacement characters  Then  the converted and unconverted text will be unequal   See this for more discussion  https   dev mysql com doc refman 8 0 en charset-repertoire html  You can use any character set name you wish in place of ASCII  For example  if you want to find out which characters won t render correctly in code page 1257  Lithuanian  Latvian  Estonian  use CONVERT columnToCheck USING cp1257

User · Answer

This is probably what you re looking for   select   from TABLE where COLUMN regexp     -       It should return all rows where COLUMN contains non-ASCII characters  or non-printable ASCII characters such as newline

User · Answer

One missing character from everyone s examples above is the termination character   0    This is invisible to the MySQL console output and is not discoverable by any of the queries heretofore mentioned  The query to find it is simply   select   from TABLE where COLUMN like    0

User · Answer

for this question we can also use this method     Question from sql zoo  Find all details of the prize won by PETER GR  NBERG  Non-ASCII characters  ans  select from nobel where winner like P  GR   berg

User · Answer

zende s answer was the only one that covered columns with a mix of ascii and non ascii characters  but it also had that problematic hex thing  I used this   SELECT   FROM  table  WHERE NOT  column  REGEXP     -      AND  column

User · Answer

Based on the correct answer  but taking into account ASCII control characters as well  the solution that worked for me is this   SELECT   FROM  table  WHERE NOT  field  REGEXP      x00-  xFF         It does the same thing  searches for violations of the ASCII range in a column  but lets you search for control characters too  since it uses hexadecimal notation for code points  Since there is no comparison or conversion  unlike  Ollie s answer   this should be significantly faster  too   Especially if MySQL does early-termination on the regex query  which it definitely should    It also avoids returning fields that are zero-length  If you want a slightly-longer version that might perform better  you can use this instead   SELECT   FROM  table  WHERE  field   lt  gt     AND NOT  field  REGEXP      x00-  xFF      It does a separate check for length to avoid zero-length results  without considering them for a regex pass  Depending on the number of zero-length entries you have  this could be significantly faster   Note that if your default character set is something bizarre where 0x00-0xFF don t map to the same values as ASCII  is there such a character set in existence anywhere    this would return a false positive  Otherwise  enjoy

User · Answer

MySQL provides comprehensive character set management that can help with this kind of problem   SELECT whatever   FROM tableName   WHERE columnToCheck  lt  gt  CONVERT columnToCheck USING ASCII    The CONVERT col USING charset  function turns the unconvertable characters into replacement characters  Then  the converted and unconverted text will be unequal   See this for more discussion  https   dev mysql com doc refman 8 0 en charset-repertoire html  You can use any character set name you wish in place of ASCII  For example  if you want to find out which characters won t render correctly in code page 1257  Lithuanian  Latvian  Estonian  use CONVERT columnToCheck USING cp1257

User · Answer

zende s answer was the only one that covered columns with a mix of ascii and non ascii characters  but it also had that problematic hex thing  I used this   SELECT   FROM  table  WHERE NOT  column  REGEXP     -      AND  column

User · Answer

Based on the correct answer  but taking into account ASCII control characters as well  the solution that worked for me is this   SELECT   FROM  table  WHERE NOT  field  REGEXP      x00-  xFF         It does the same thing  searches for violations of the ASCII range in a column  but lets you search for control characters too  since it uses hexadecimal notation for code points  Since there is no comparison or conversion  unlike  Ollie s answer   this should be significantly faster  too   Especially if MySQL does early-termination on the regex query  which it definitely should    It also avoids returning fields that are zero-length  If you want a slightly-longer version that might perform better  you can use this instead   SELECT   FROM  table  WHERE  field   lt  gt     AND NOT  field  REGEXP      x00-  xFF      It does a separate check for length to avoid zero-length results  without considering them for a regex pass  Depending on the number of zero-length entries you have  this could be significantly faster   Note that if your default character set is something bizarre where 0x00-0xFF don t map to the same values as ASCII  is there such a character set in existence anywhere    this would return a false positive  Otherwise  enjoy

User · Answer

for this question we can also use this method     Question from sql zoo  Find all details of the prize won by PETER GR  NBERG  Non-ASCII characters  ans  select from nobel where winner like P  GR   berg

User · Answer

You can define ASCII as all characters that have a decimal value of 0 - 127  0x00 - 0x7F  and find columns with non-ASCII characters using the following query  SELECT   FROM TABLE WHERE NOT HEX COLUMN  REGEXP     0-7  0-9A-F         This was the most comprehensive query I could come up with

[mysql] How can I find non-ASCII characters in MySQL?

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