MSSQL aggregate ignoring where clause - sql-server

Question

I have a strange problem that when performing an aggregate function on a type cast varchar column I receive an "Msg 8114, Level 16, State 5, Line 1. Error converting data type nvarchar to bigint." The queries where clause should filter out the non-numeric values.
Table structure is similar to this:
IF EXISTS (SELECT * FROM sys.all_objects ao WHERE ao.name = 'Identifier' AND ao.type = 'U') BEGIN DROP TABLE Identifier END
IF EXISTS (SELECT * FROM sys.all_objects ao WHERE ao.name = 'IdentifierType' AND ao.type = 'U') BEGIN DROP TABLE IdentifierType END
CREATE TABLE IdentifierType
(
[ID] [int] IDENTITY(1,1) NOT NULL,
[Style] [int] NULL,
CONSTRAINT [PK_IdentifierType_ID] PRIMARY KEY CLUSTERED ([ID] ASC)
) ON [PRIMARY]
CREATE TABLE Identifier
(
[ID] [int] IDENTITY(1,1) NOT NULL,
[IdentifierTypeID] [int] NOT NULL,
[Value] [nvarchar](4000) NOT NULL,
CONSTRAINT [PK_Identifier_ID] PRIMARY KEY CLUSTERED ([ID] ASC)
) ON [PRIMARY]
ALTER TABLE Identifier WITH CHECK ADD CONSTRAINT [FK_Identifier_IdentifierTypeID] FOREIGN KEY([IdentifierTypeID]) REFERENCES IdentifierType ([ID])
GO
Identifier.Value is a VARCHAR column, it can and does contain non-numeric data. Filtering the query to IdentifierType.Style = 0 should mean that 'Value' only returns string representations of integers. The query below fails with "Msg 8114, Level 16, State 5, Line 1. Error converting data type nvarchar to bigint."
SELECT
MAX(CAST(Value AS BIGINT))
FROM
Identifier i,
IdentifierType it
WHERE
i.IdentifierTypeID = it.ID AND
it.Style = 0
If i extend the WHERE clause to include a 'AND ISNUMERIC(i.Value) = 1' it will return the maximum integer value. That to me implies that there is a non-numeric string in my result set. Yet i get no rows returned from this:
SELECT
*
FROM
Identifier i,
IdentifierType it
WHERE
i.IdentifierTypeID = it.ID AND
it.Style = 0 AND
ISNUMERIC(i.Value) <> 1
I've been unable to identity the row(s) that are tripping the type cast. The above query should have exposed the exceptional rows. In addition, there are no empty or extremely long strings either (the largest string is 6 character long)
Is it possible that MSSQL is attempting to do the CAST on all rows rather than filtering via the WHERE clause first?
Or has anyone else seen anything similar?
There is a second work around which is instantiating the component of the query into a temp table, and then selecting the MAX value from that.
SELECT
Value
INTO
IdentifierClone
FROM
Identifier i,
IdentifierType it
WHERE
i.IdentifierTypeID = it.ID AND
it.Style = 0
SELECT MAX(CAST(Value as BIGINT)) FROM IdentifierClone
A subquery doesn't work however.
Any help or thoughts would be appreciated.

Answer 1

Try using a REGEX expression to find the problem record. Here's an example where ISNUMERIC does not detect the problem but the regex expression does
CREATE TABLE tst (value nvarchar(4000))
INSERT INTO tst select '£'
-- Record found ...
SELECT * FROM tst WHERE value NOT LIKE '%[0-9]%'
-- No record found ...
SELECT * from tst where isnumeric(value) <> 1