SDB ToDo list (and general notes)
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+ Prepared statement query cache?
  When will it be beneficial - GraphSDB?

+ Value-based hashing
  String version - and have fixed choice of xsd:string or plain string for terms.
  Partial alternative: condition is "T.o = hash1 OR T.o = hash2"

+ Features: more general config setting?
  Or really use properties?
  layout; layout/index; layout/hash for now.

+ Generating SQL:
  + Precedence-driven output for SqlExpr // SqlExprGenerateSQL, not lots of nesting.
  + SELECT/one table ==> move constraints out (it's just SPJ)
    Put in a SqlNode optimizer stage, just before generation
      IJ-R-T => IJ(r)-T is done specially 
    
+ Features:
  In desc file for now.
  Features are params to layout

+ Values and conditions : reactivate condition compilation.
  Need value access
  Isolate QC2.insertValueGetter

+ Ugly Store.getNodeKeyColName()

+ Term tests : check there is a test for ' quotes

+ Script library

+ cmd: 
  @ --load for sdb.sdbquery --format
     Done - but should be ModData/ModInit/ModSetup
     
+ Add query tests :
  /Structure/ { opt ... } JOIN { opt ... } 
  
+ Abstracting databases:
  Graph for an SDBConnection (or get from DB).
    That is the unit of database if there are multiple stores per connection.
    Or maybe a Store features?
      A/ regex syntax
      B/ Table exists code (Classes, Value tables etc).

+ ValueTables
  String value table
    With no URIs, much shorter.
    Full text indexing where available?

+ Graph pattern tables

+ Abstract columns types then simple templating.
        VARCHAR/TEXT/BLOB abstract syntax