We are converting a STRING field to a DATETIME field using BigQuery's non-legacy SQL.
The DATETIME fields are corrupted with values like "None" and "0.0" which causes our CAST statement to fail.
We see that for other types of SQL there are TRY-CATCH functions and ISNUMERIC() tests - neither of which appear to be supported in BigQuery.
Here's an example that catches "None" but fails to catch random floats or integers:
CASE
WHEN UPDT_DT_TM LIKE 'None' THEN NULL
ELSE CAST(UPDT_DT_TM AS DATETIME)
END AS UPDT_DT_TM,
Apart from User-Defined-Functions (UDF) in BigQuery - is there any other way in create a CASE statement that can convert to DATETIME when it can but otherwise just leaves the value as NULL?
You can use the SAFE_CAST function, which returns NULL if the input is not a valid value when interpreted as the desired type. In your case, you would just use SAFE_CAST(UPDT_DT_TM AS DATETIME). It is in the Functions & Operators documentation.
Related
I have been trying to update a datetime column using the following SQL Statement:
UPDATE HistoricData SET RecordDate=DATETIME(RecordDate,'60 minutes') WHERE DataStreamID=1 AND TimeFrameID=5
However, I keep getting the following error message:
NOT NULL Constraint Failed: HistoricData.RecordDate
If you could recommend the appropriate change to get this working, I would very much appreciate it.
I will attempt to attach a sample schema and data:
Table Data
Table Schema
After inspecting your DML, my only remaining concern was the datetime format you have in your table. I tried updating such a value as you did, and guess what, it returns NULL: http://sqlfiddle.com/#!7/f4651/10 Why? Because your strings (do notation) are not valid ISO-8601 strings. You probably need to simply replace the dots with dashes before updating (http://sqlfiddle.com/#!7/f4651/11).
When reading date fields from Sqlite into Firedac, I get conversion errors. The fields are called dates but with string entries (yyyy-mm-dd). I set the option for Datetime Format = string, but I've discovered that while null values are handled OK, empty values (= '') produce an error which I can't figure out how to handle.
You can enable StrsEmpty2Null option, which will automatically convert all empty strings to NULL state. But it's for all values and parameters handled by the data component. So it's not the cure.
I'm not sure what you're doing, but in general, NULL is a state and you cannot convert NULL state to a value because it's a state indicating no value. So as you cannot convert empty string to date.
So try to describe more about your value to string conversion, so we can suggest a proper way to deal with it. For SQLite, I'd suggest using DATE pseudo data type and convert values through the built-in formatting expressions.
I am using SQLite and NHibernate and Im storing my date as Strings on SQLite since I cant store as Date.
Everything was just fine until a need to compare dates.. I tried the following codes:
var initialDate = DateTime.Parse(_InitialDate);
var finalDate = DateTime.Parse(_FinalDate);
return session.QueryOver<Locacoes>()
.Where(c => DateTime.Parse(c.InitialDate) >= initialDate )
.Where(c => DateTime.Parse(c.FinalDate) <= finalDate).List();
but I got an exception on the first "Where": "a variable 'c' of type 'Locacoes' is referenced on scope '', but it is not defined".
How can I compare date on SQLite using NHibernate?
I've tried many things with above code, but didnt work.
Edit: Its not duplicate, the error can be the same, but the result is different
First, while Sqlite likes to pretend everything is a string, that should be considered a storage format and NO REASON why your object model should use strings to hold date values. Your object model should of course type the properties as DateTime or DateTimeOffset. Then configure your NHibernate mappings properly to map the values to what SQLite can handle (actually I think NHibernate would handle that automatically if you just tell it to use the SQLiteDialect).
Second, I don't think QueryOver() can handle things like DateTime.Parse(). Don't confuse QueryOver() with Linq2NHibernate (the Query() method), which have more advanced expression interpretation abilities. On the other hand, you no longer need to use Parse() when you begin to use correct types in your object model.
At least if you use LINQ, it should be able to handle DateTime.Date for SQLite, if you need it:
session.Query<Locacoes>()
.Where(l => c.InitialDate.Date >= initialDate)
Of course, you would only need to put Date in there if there is a non-zero time-of-day component that you need to ignore.
SQLite doesn't really have date columns. You can store your dates as ISO-8601 strings, or as the integer number of seconds since the epoch, or as Julian day numbers. In the table I'm using, I want my dates to be human-readable, so I've chosen to use ISO-8601 strings.
Suppose I want to query all the records with dates after today. The ISO-8601 strings will sort properly, so I should be able to use string comparison with the ISO-8601 string for today's date.
However, I see no way to do the comparison using the F# SqlProvider type provider. I'm hoping that this is just a reflection of my lack of knowledge of F# query expressions.
For instance, I can't do:
query {
for calendarEntry in dataContext.``[main].[calendar_entries]`` do
where (calendarEntry.date >= System.DateTime.Today.ToString("yyyy-MM-dd hh:mm:ss"))
... }
I get:
The binary operator GreaterThanOrEqual is not defined for the types 'System.String' and 'System.String'.
I also can't do any variation of:
query {
for calendarEntry in dataContext.``[main].[calendar_entries]`` do
where (calendarEntry.date.CompareTo(System.DateTime.Today.ToString("yyyy-MM-dd hh:mm:ss")) >= 0)
... }
I get:
Unsupported expression. Ensure all server-side objects appear on the left hand side of predicates. The In and Not In operators only support the inline array syntax.
Anyone know how I might do string comparisons in the where clause? It seems that my only option for filtering inside the query is to store seconds-since-epoch in the database and use integer comparisons.
This was a temporary bug with old SQLProvider version and it should be working now. If not, please open a new issue to the GitHub repository: https://github.com/fsprojects/SQLProvider
How do I check if data existing in the database or is NULL. I'm getting the following error Object cannot be cast from DBNull to other types . Do I need to add IsDBNULL to the code?
SignedOn.Text = Convert.ToDateTime(reader("SignedOn")).ToShortDateString()
you can check like below
If NOT IsDbNull(reader("SignedOn")) Then
SignedOn.Text = Convert.ToDateTime(reader("SignedOn")).ToShortDateString()
End If
Edit based on comments:
When you know the exact type of the column you can call method relevant to that type like reader.GetDateTime, reader.GetString etc
After conversion if there is a possibility of result can be null then you better check for null before calling ToShortDateString
You can use DateTime.TryParse method if you have store date time in varchar column